Error message: Unable to start debugging on the web server

Unable to start debugging on the web server. The web server is not configured correctly. See help for common configuration errors. Running the web page outside of the debugger may provide further information. Click Help for more information

You get the above error message when you start your ASP program.

In web.config file, if compilation debug is false, you should change it to true. That is one of the issues that can generate such error message.

<compilation debug="true">

Another reason can be Network service or Aspnet user (depending on the operating system)doesn't have read and write permissions on the following folder (for framework 2):
C:\WINDOWS\Microsoft.NET\Framework\v2.0.50727\Temporary ASP.NET Files