BUG: "Unable to start debugging on the Web server" error message when you run an ASP.NET Web application


You create an ASP.NET Web application by using localhost as the Web server, and you change the Web site setting in Microsoft Internet Information Services (IIS) to use the specific IP address for Web Site Identification. Then, when you run the application, you receive the following error message:
Error while trying to run project: Unable to start debugging on the web server. Could not start ASP.NET or ATL Server debugging.

Verify that ASP.NET or ATL Server is correctly installed on the server.


This problem occurs because the debugger does not send the debug action to IIS when you run the application. The debugger identifies your computer as localhost. However, in IIS, the Web Site Identification of the application is the IP address that you specified.


  1. In a text editor such as Notepad, open the
    WebApplicationName.vbproj.webinfo file.

    Note In a Visual C# .NET project, this is the WebApplicationName.csproj.webinfo file.

    This file is located in the application folder for the application project.
  2. Locate the following line.

    Visual Basic .NET
     <Web URLPath = "http://localhost/<WebApplicationName>/<WebApplicationName>.vbproj" /> 
    Visual C# .NET
     <Web URLPath = "http://localhost/<WebApplicationName>/<WebApplicationName>.csproj" /> 
  3. Replace "localhost" with the IP Address of your computer as follows.

    Visual Basic .NET
     <Web URLPath = "<WebApplicationName>/<WebApplicationName>.vbproj" /> 
    Visual C# .NET
     <Web URLPath = "<WebApplicationName>/<WebApplicationName>.csproj" /> 
  4. Start Microsoft Internet Explorer. On the
    Tools menu, click Internet Options.
  5. In the Internet Options dialog box, click the Security tab. Under Select a Web content zone to specify its security settings, click Local Intranet, and then click Sites.
  6. In the Local Intranet dialog box, click
  7. In the Add this Web Site to the zone box, type the URL of your project, and then click Add.
  8. Close the application, and then open the application again.
  9. On the Debug menu, click


Microsoft has confirmed that this is a bug in the Microsoft products that are listed in the "Applies to" section.

More Information

Steps to reproduce the problem

  1. In Microsoft Visual Studio .NET, create a new Web Application project or a new Web site project by using Visual Basic .NET or Visual C# .NET. In the New Project dialog box, type
    http://localhost/testapp in the
    location box.
  2. Click Start, click Run, type inetmgr, and then click OK.
  3. In Internet Information Services (IIS) Manager, expand
    (local computer), and then locate Default Web Site.
  4. Right-click Default Web Site, and then click Properties.
  5. In the Default Web Site Properties dialog box, click the Web Site tab. In the IP address list, click the IP address of your computer. Click
    OK, and then close IIS Manager.
  6. On the Debug menu, click


For more information, visit the following Microsoft Developer Network (MSDN) Web site: