How To Troubleshoot DCOM for Visual Basic Client/Server Applications

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SUMMARY

This article describes various steps you can take to troubleshoot some of the most common errors you encounter when you try to instantiate a remote server object by using Distributed Component Object Model (DCOM). In Visual Basic, the most common error messages are:
Run-time error 70: Permission Denied.
Run-time error 429: ActiveX component can't create object.
Run-time error 462: The remote server computer does not exist or is unavailable.

MORE INFORMATION

Where to Start Troubleshooting

Most of the problems that occur when you try to instantiate a COM object on a remote computer by using DCOM are related to incorrect settings in Dcomcnfg or a networking problem. Very seldom is the problem related to the code.

The first thing to do is to write down the information related to your environment and the application itself, such as:
  1. About the server computer:

    The server computer is the computer where the server application is going to run. Collect the following data:
    • Operating system and installed service pack.
    • Is somebody logged on to the computer?
    • If somebody is logged on, what are their rights? Are they part of the Administrators group? Are they logged on as a Domain User?
  2. About the client computer:

    The client computer is the computer where the client application is going to run. Collect the following data:
    • Operating system and installed service pack.
    • Who is logged on to this computer? Did they logged on as a Domain User or as a Local User? If they logged on as a Domain User what are their rights on the server computer? Are they part of the Administrators group on the server computer?
  3. About the server application:
    • With which language, version, and service pack was the server developed?
    • Does it call back to the client?
    • Does it raise events? If so, is DCOM security set on the client computer to grant access to the Everyone account?
    • Does it have a user interface?
    • Is it marked as Unattended Execution?
    • Is it setting security parameters programmatically through the call of functions such as CoInitializeSecurity or CoSetProxyBlanket?
  4. About the client application:
    • With which language, version, and service pack was the application developed?
    • Is it setting security parameters programmatically through the call of functions such as CoInitializeSecurity or CoSetProxyBlanket?
  5. About the network:
    • Are the client and the server computers on the same Local Area Network (LAN)?
    • Are the client and the server computers connected through the Internet, without firewalls and proxies between them?
    • Are the client and the server computers connected through the Internet, with firewalls and proxies between them?

Basic Troubleshooting

  1. Check that all of the settings in Dcomcnfg are appropriate, based on the data you collected earlier.
    268550 How To Use Dcomcnfg for a Visual Basic DCOM Client/Server Application
  2. If you are using Microsoft Windows 95 on the client or server computer, ensure that you have installed DCOM95 on it. You can download DCOM95 from the following Microsoft Web site:
    http://www.microsoft.com/com/dcom/dcom95/download.asp
  3. If you are using Windows 95, Microsoft Windows 98, Windows Millennium Edition (Me) on the server computer, you need to have the server component running before you try to use the client. As a check, verify that the server is running and that it is waiting for the client to connect.
    165101 How To Use Windows 95, Windows 98, or Windows Me as a DCOM Server
  4. If your client and server computers are connected through the Internet with firewalls and proxies between them, DCOM does not work if there is any type of Address Translation (NAT) in between them. If there is no address translation, you need to configure these proxies and firewalls to enable DCOM to communicate. You can find several white papers related to this subject on the Microsoft Developers Network (MSDN) or at the following Microsoft Web site:
    http://www.microsoft.com/technet/prodtechnol/windows2000serv/reskit/cnet/cnad_arc_wbak.mspx?mfr=true
    This subject is not covered in this article.

Additional Troubleshooting

If you still have problems after setting Dcomcnfg to the right settings based on your environment and application features, here are several additional steps you can take to solve your problem:
  1. Use Task Manager to verify that the server is not running while you make changes in the settings using Dcomcnfg. All settings are assigned to a process when it starts so, if the server is running while you change the settings, the new settings only take effect the next time the server is launched.
  2. Verify that the server and client run correctly on the same computer. You should always test that your client and server run correctly locally; that is, on the same computer, before running remotely.
  3. Check if the problem you are facing is really a DCOM issue, which is usually not related to the code itself, or if it's a coding issue specific to your application. Do this by creating a very simple client/server application with just one or two very simple methods. Follow the normal procedures of packaging and installation. If your server raises events, then your small sample should also raise events. For additional information, click the article numbers below to view the articles in the Microsoft Knowledge Base:
    266717 How To Create a DCOM Client/Server Application by Using Visual Basic
    267836 How To Create a DCOM Client/Server with Events by Using Visual Basic
    Ideally, you should use the preceding articles as a guideline because they take you step-by-step from scratch through to the final packaging and deployment. Use the same settings as you are using for your application and see if this works. If your problem is related to DCOM, you face the same problems on the small sample as you do in your application. Keep troubleshooting the problem with the small sample until you find the problem. If the small application works fine but your own application doesn't work with the same settings, then you can be facing two problems:
    • Something in your code is creating the problem. For example, if you access a database in your code and the identity of your server doesn't have rights to do so. The same problem can happen if you are trying to access files or instantiate other objects.
    • Your code is fine, but you have some problems in the Registry, such as multiple entries to your server. For additional information, click the article number below to view the article in the Microsoft Knowledge Base:
      180525 PRB: Dcomcnfg Reports Multiple Copies of DCOM Server
    • You are pointing the client computer to the wrong server computer. Check the location tab in Dcomcnfg on the client computer.For additional information, click the article number below to view the article in the Microsoft Knowledge Base:
      268550 How To Use Dcomcnfg for a Visual Basic DCOM Client/Server Application
  4. Verify that you have packaged and installed the client and the server correctly. Creating the distribution packages correctly is fundamental to a successful installation.For additional information about a step-by-step sample on how to create a DCOM client/server application using Visual Basic, click the article numbers below to view the articles in the Microsoft Knowledge Base:
    266717 How To Create a DCOM Client/Server Application by Using Visual Basic
    267836 How To Create a DCOM Client/Server with Events by Using Visual Basic
  5. Verify that your network is working correctly by pinging the client from the server computer and the server from the client computer. On the server computer, open a command prompt window, and execute the following command where the preceding ClientcomputerName should be the name of your client computer:
    Ping ClientcomputerName
    If everything is working correctly, you should see three or four replies and the time each one took. If you see timeouts or other errors, you have problems in your network setup and you need to fix these before you can continue. Repeat the same steps on the client computer using the server's computer name.
  6. In Dcomcnfg on the client computer, change the server's location by replacing the server's name with the server's IP address. If it works with the IP address and not with the server's computer name, then more than likely you have problems with your networking settings.
  7. Try to restart the server and client. Sometimes some settings are cached in memory and restarting after making changes in Dcomcnfg solves the problem.
  8. On Windows 95 or Windows 98, use the TCP/IP protocol. To do this, remove all other protocols in the default protocols list in Dcomcnfg.
  9. Usually, if you have a DCOM problem, you get an error when you try to instantiate the remote object by calling the CreateObject function or when you set the object variable with the New keyword. It's important to be able to distinguish if you are getting an error message due to the creation of the object itself, or due to what you are doing in the Initialize event of the object. If the Initialize event of the object you are trying to instantiate doesn't have any code, then there is no doubt that the error you are getting is related to the instantiating of your object. If, however, you have code in the Initialize event, such as connecting to a database or instantiating other objects, you should include error trapping inside the Initialize event and raise a custom user error. If you don't trap your errors inside the Initialize event and an error is raised, it bubbles out to the client and may confuse you. You may think that the problem is the object creation when the problem is actually the code in the Initialize event.
  10. If the server is running on Microsoft Windows NT 4 or Microsoft Windows 2000, you can use the Event Viewer to find out additional auditing information on why the DCOM connection failed. However, logging these type of events is usually not enabled by default. You need to set the auditing options to enable it.

    In Windows NT 4, enable these options as follows:

    • On the Start menu, select Programs, select Administrative Tools, and then select User Manager.
    • If you are running NT 4 server, you must select a domain; in this case, on the User menu, select the Domain option, and then select your local computer.
    • On the Policies menu, select the Audit option. Enable auditing for both success and failure for the first three entries: Logon/Logoff, File and Object Access, Use of User Rights. Click OK and close User Manager.

    In Windows 2000, enable these options as follows:

    • On the Start menu, select Programs, select Administrative Tools, and then select Local Security Policy.
    • On the left-hand pane, you see a tree view. Click the plus (+) sign at the left of the Local Policies, and you see the Audit Policy entry. Select the Audit Policy entry, and note that the right pane contains all audit options, which one is enabled and which one is not. Right-clicking at any of these options allows you to enable or disable them.
    • Enable auditing for success and failure for the following options: Audit logon events, Audit object access, Audit privilege use.
    • Close the Local Security Policy window.

    Once you have activated these logging options, test your client again. After you get the error message, use Event Viewer to see if there are any DCOM events. The event may tell you why access was denied. Also, it can tell you who is logged on to the client computer and if this is a domain user or a local user. It can tell you that the protocol requested by the client is not available on the server, and so forth. COM logs are usually added to the system log.
  11. If your server has more than one class, and some of these classes work and others don't, check each class entry in Dcomcnfg on the client computer. By default, each class has its own AppID and, consequently, its own settings, so it's possible that some of your classes are set correctly and others are not. For additional information about Locating your server in the client's application list, click the article number below to view the article in the Microsoft Knowledge Base:
    268550 How To Use Dcomcnfg for a Visual Basic DCOM Client/Server Application

Run-Time Error 70: Permission Denied

This error is usually related to security settings. This error is a good indication that the call reached the target computer, so networking is probably not a problem here. Here are a few things to check:
  • If you set the authentication level to Connect, verify that the user logged in to the client computer is logged in as a domain user and not a local user.
  • If you set the authentication level to Connect, verify that the server computer actually belongs to the domain. If it's a standalone computer, it cannot authenticate the users unless you have a matching user name/password on both the client and server computer.
  • If you set the authentication level to None, check if you've set this option to none on both client and server computers.
  • If you set the authentication level to None and you have verified that both computers have this setting correct, be sure that neither the client nor the server application is setting authentication programmatically using functions such as CoInitializeSecurity or CoSetProxyBlanket. Setting authentication programmatically overrides the registry entries from Dcomcnfg.
  • If you set the authentication level to None, and you have non-domain users, check if you have included "Everyone" (or "The World" for Windows 95 and Windows 98) in the access and launch permissions.
  • Check the access and launching permissions in Dcomcnfg and verify that the user logged on to the client computer is explicitly included in these lists, or belongs to one of the groups included.
  • See "Known Issues to Check" later in this article.For additional information, click the article number below to view the article in the Microsoft Knowledge Base:
    216051 FIX: Dcomcnfg NT 4.0 SP4 Does Not Write .Exe File Name Under HKCR\APPID

Run-Time Error 429: ActiveX Component Can't Create Object

Following are a few things that could cause this error:
  • The server is not correctly installed on the server computer. Run Dcomcnfg on the server computer, select the server application on the list of applications, and then click Properties. In the Location tab, verify that the only option checked is Run application on this computer.
  • You recompiled the server without binary compatibility, and didn't recompile the client. The client may be looking for old class IDs. Even if you recompiled the client, you may have multiple entries in the registry, old ones and new ones.For additional information, click the article number below to view the article in the Microsoft Knowledge Base:
    180525 PRB: Dcomcnfg Reports Multiple Copies of DCOM Server
  • You may be using the wrong server name in the location tab. For example, you installed the server on computer ServerA, and for some reason you defined the location in Dcomcnfg as being ServerB. Run Dcomcnfg on the client computer, locate the server on the list of applications, and then click Properties. Select the Location tab, and then verify that the server computer name is correct. If you are unable to locate your server in the list of applications, look for "Locating your server in the client's applications list" in the following Microsoft Knowledge Base article:
    268550 How To Use Dcomcnfg for a Visual Basic DCOM Client/Server Application
  • Also see "Known Issues to Check" later in this article.For additional information, click the article number below to view the article in the Microsoft Knowledge Base:
    193143 BUG: DCOM Client Hangs and Then Gives Error Message 429

Error 462: The Remote Server Computer Does Not Exist or Is Unavailable

Following are some causes for this error message:
  • You may be using the wrong server name in the location tab. For example, you installed the server on computer ServerA, and for some reason you defined the location in Dcomcnfg as being ServerB, and ServerB is not a valid computer. Run Dcomcnfg on the client computer, locate the server on the list of applications, and then click the Properties button. Select the Location tab, and then verify that the server computer name is correct. If you are unable to locate your server in the list of applications, see "Locating your server in the client's applications list" in the following Microsoft Knowledge Base article:
    268550 How To Use Dcomcnfg for a Visual Basic DCOM Client/Server Application
  • Ping the server from the client and verify that it is reachable. Also ping the client from the server to see if it is reachable. Ping by name and IP address. See item 5 in the "Additional Troubleshooting" section of this article.
  • Your server is running on a Windows 95, Windows 98, or Windows Me computer, and the server is not running waiting for clients to connect, or RPCSS.EXE is not running.For additional information on this topic, click the article number below to view the article in the Microsoft Knowledge Base:
    165101 How To Use Windows 95 or Windows 98 as a DCOM Server
  • Your computer has more than one network card.For additional information on this topic, click the article number below to view the article in the Microsoft Knowledge Base:
    183930 FIX: IP Is Mangled When Using UDP on Multihomed Computers
  • Please see the "Known Issues to Check" section of this article.
  • The server computer is not running or is still in its reboot state.

The Server Hangs

If your server does not have a user interface, verify that you checked the Unattended Execution option. If you don't check this option, it's possible that a message box is being displayed by your server due to an untrapped error, for example. If your server is not running with the identity Interactive User, nobody can see this message box and the server is just waiting for somebody to dismiss the box, which never happens. By using the Unattended Execution option, message boxes are redirected to a log file.

Client Crashes After Installation

For additional information about this topic, click the article numbers below to view the articles in the Microsoft Knowledge Base:
185193 PRB: Clireg32 Fails to Register the Type Library of DCOM Server
221173 PRB: Installing VB6 Does Not Update Clireg32.exe

Known Issues to Check

Following is a list of known problems that could be affecting your installation. They are documented in other Microsoft Knowledge Base articles. Their article IDs are provided here. If you are still having problems with your DCOM application after reviewing the troubleshooting steps in this article and the list of known issues, be sure to search the Knowledge Base for additional articles that may not be included in this article.
  1. The following error message affects server applications created with Visual Basic 6.0 Initial Release, before Service Pack 1.
    193143 DCOM Client Hangs and Then Gives Error Message 429
  2. The following problem was introduced in the Dcomcnfg that shipped with Service Pack 4 for NT 4.0 and fixed in Service Pack 6 for NT 4.0. However, even if you already have the fixed version shipped with SP6 but your server was installed before you installed SP6, you may still be experiencing this problem. The problem is that Dcomcnfg did not include one needed registry key under Hkey_Classes_Root\AppID. The HKCR\AppID is the key that maps the executable of a server to its AppID. For example, if your server's executable is MyServer.exe, there must be a key under HKCR\AppID with this name. One of the values under this key should be AppID that contains the AppID GUID of your server. See instructions in the following Microsoft Knowledge Base article on how to add the missing entry manually.
    216051 Dcomcnfg NT 4.0 SP4 Does Not Write .Exe Name Under HKCR\APPID
    The consequence of this error is that the system ignores all custom entries that you defined in Dcomcnfg for this server. For example, if you defined a list of users that has rights to access and launch your server, and this list includes User1, but you still get error 70 "Access Denied" when User1 tries to connect to your server, chances are you have this problem. Another problem, for example, is if you defined the Identity of your server to be Interactive User, but the server continues to behave as if it has Identity Launching User - which is the default.
  3. There was a bug in Clireg32.exe that shipped with Visual Basic 5.0. The consequence was that the client crashed after installation. The version of Clireg32 shipping with Visual Basic 6.0 has this bug fixed, but if you had the old version on the computer when you installed Visual Basic 6.0, the installation procedure does not update the file, so you may have the old version.

    Clireg32.exe is a utility that registers the VBR and TLB files in the client computer. When you create a distribution package for a client and add a VBR file, the Package and Deployment Wizard (PDW) automatically adds Clireg32.exe to your distribution package. If you have the bad version of clireg32.exe on your development computer, you may be distributing the bad version with your application. If the target computer doesn't already have a newer version, this bad version is the one that is being used. The version with problems that shipped with Visual Basic 5.0 is 5.00.3716, dated 1/16/1997 12:00.
    185193 Clireg32 Fails to Register the Type Library of DCOM server
    221173 Installing VB6 Doesn't Update Clireg32.exe
  4. The following bug can cause problems when you are using DCOM on a computer with more than one network card. One possible error message is:
    462 Remote server computer is unavailable.
    To avoid this problem, keep only TCP/IP on the list of protocols on this computer. This issue is fixed in NT4 SP4.
    183930 IP Is Mangled When Using UDP on Multihomed Computers
  5. When a COM client on a Windows NT computer runs under an identity that cannot be authenticated on the remote computer, a COM server started by the client shuts down in approximately six minutes.
    175020 Remote COM Server Shuts Down After Six Minutes

Properties

Article ID: 269330 - Last Review: January 31, 2007 - Revision: 2.5
APPLIES TO
  • Microsoft Visual Basic 5.0 Enterprise Edition
  • Microsoft Visual Basic Enterprise Edition for Windows 6.0
Keywords: 
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