Error message when Outlook 2003 users connect to Exchange Server 2003 by using RPC over HTTP: "Server Unavailable"

In a Microsoft Exchange Server 2003 organization, Microsoft Office Outlook 2003 users receive the following error message when they connect to Exchange Server 2003 by using RPC over HTTP:Additionally, the following errors are logged in the Internet Information Services (IIS) logs on the RPC proxy server:

This problem occurs if the RPC proxy server extensions do not load correctly.

To resolve this problem, verify in IIS Manager that the path of the Rpcproxy.dll file is valid. Additionally, verify that the file is located in the correct path and that the file is registered correctly. To do this, follow these steps.

Step 1: Verify the location of the Rpcproxy.dll file

1. Verify that the Rpcproxy.dll file is located in the following folder:
   Drive_Letter:\Windows\system32\rpcproxy\rpcproxy.dll
   Note If the Rpcproxy.dll file is located in this folder, go to step 2.
2. If you cannot locate the file in step 1a, locate the Rpcproxy.dll file in the following folder:
   Drive_Letter:\Windows\system32\dllcache
   Note The dllcache folder is a hidden folder. To see this folder, enable the Show hidden files and folders option in Windows Explorer.
3. Copy the file from the dllcache folder to the rpcproxy folder.

Step 2: Verify the registered path in IIS Manager

1. Start IIS Manager.
2. Click Web Service Extensions.
3. In the right pane, right-click RPC Proxy Server Extension, and then click Properties.
4. On the General tab, verify that the path of the Rpcproxy.dll file resembles the following:
   Drive_Letter:\Windows\system32\rpcproxy\rpcproxy.dll
   Note If the path is incorrect, go to step 2e. If the path is correct, go to step 3.
5. Click the Required Files tab.
6. In the Files window, click the existing entry for the Rpcproxy.dll file, and then click Remove.
7. Click Add.
8. In the Path to file box, type Drive_Letter:\Windows\system32\rpcproxy\rpcproxy.dll. Alternatively, you can click Browse to locate the specified folder. Then, click the file, and then click Open.
9. Click OK.
10. Exit IIS Manager.
11. Use Outlook 2003 to connect to Exchange Server 2003.

Step 3: Replace and register the Rpcproxy.dll file

If you receive the error message that is mentioned in the "Symptoms" section, the Rpcproxy.dll file may be corrupted. Alternatively, the Rpcproxy.dll file may not be registered correctly. This problem may occur even though the path is correctly specified in the properties of the RPC proxy server extension object. To correct this problem, follow these steps:

1. Replace the Rpcproxy.dll file in the Drive_Letter:\Windows\system32\rpcproxy folder by using the file from the following folder:
   Drive_Letter:\Windows\system32\dllcache
2. To do this, click Start, click Run, type regsvr32 Drive_Letter:\Windows\system32\rpcproxy\rpcproxy.dll, and then click OK.
3. Use Outlook 2003 to connect to Exchange Server 2003.