This article was previously published under Q318465
When you debug an ASP.NET application in Microsoft Visual Studio .NET, you may receive the following Microsoft Development Environment error message:
Error while trying to run project: Unable to start debugging on the web server. The server does not support debugging of ASP.NET or ATL Server applications. Run setup to install the Visual Studio .NET server components. If setup has been run, verify that a valid URL has been specified.
You may also want to refer to the ASP.NET and ATL Server debugging topic in the online documentation. Would you like to disable future attempts to debug ASP.NET pages for this project?
This error may occur if the Microsoft .NET Framework setup or installation was not completed correctly. When this occurs, the application mappings for ASP.NET file name extensions (such as .aspx) are not configured correctly in Microsoft Internet Information Services (IIS).
To check whether the application mappings are correct, follow these steps:
Click Start, point to Programs, point to Administrative Tools, and then click Internet Services Manager.
Expand the node that corresponds to the local host (computer name), and then expand the Default Web Site node.
Right-click your Web application directory, and then click Properties.
On the Directory tab, under Application Settings, click Configuration.
Click the App Mappings tab.
On the App Mappings tab, under Application Mappings, check whether the .aspx extension is mapped to the following dynamic-link library (DLL):