You would get this error if the application mappings for ASP.NET file name extensions (such as .aspx) are not configured correctly in Microsoft Internet Information Services (IIS).
To resolve this go to C:\Windows Directory\Microsoft.Net\Framework\Version and type aspnet_regiis -i to configure the required application mappings correctly
On Trying to Debug an application, by the F5 key I get the error: "Error while trying to run project: Unable to start debugging on the web server. Catastrophic failure"?
This issue occurs if the account that is used to run the ASP.NET Worker process (by default, the ASPNET user account) is not assigned the "Impersonate a client after authentication" user right in the "Local Security Policy" settings. This issue may occur when you install Microsoft Visual Studio .NET after you install Windows 2000 Service Pack 4 (SP4) on the computer. In this situation, the ASPNET account is not assigned the "Impersonate a client after authentication" user right in the "Local Security Policy" settings.To resolve it, please use the method at: To work around the problem, manually assign Impersonate a client after authentication to the IWAM account. To do so, follow these steps:
To enforce an update of computer policy, type the following command: secedit /refreshpolicy machine_policy /enforce
At a command prompt, type iisreset. In case your server is a Domain Controller Refer PRB: "Catastrophic Failure" Error Message When You Try to Debug an ASP.NET Application on Windows 2000 Domain Controller