If while trying to debug your ASP.NET web application you receive the following error:

Error while trying to run project: Unable to start debugging on the web server. Catastrophic failure.
Would you like to disable future attempts to debug ASP.NET pages for this project?

You most probably don’t have ASP.NET registered correctly on the system in which you are trying to make the debugging. Open Run from Start Menu -> Run and type the following line:

aspnet_regiis.exe -i

After ASP.NET is registered successfully, reset IIS using the following command once again inside Run:

iisreset

For more details read the tutorial entitled Setting up your ASP.NET server (IIS).

If this doesn’t solve your problem and you are using .NET Framework 1.0, download and install .NET Framework 1.1 or .NET Framework 2.0.