For debugging Classic ASP keep in mind two key terms:-
1. Classic ASP debugging only works with IIS. It does not work with the VS Development Web Server.
2. In Visual Studio you have to attach to the ASP worker process (w3wp.exe in IIS 6,7).
Here is how to make ASP debugging work:
1. Enable ASP debugging on the server.
2. Open classic ASP in VS Studio.
3. Set breakpoint.
4. View page in browser or run without debugging.
5. Debug | Attach to Process
6. Locate IIS ASP worker process (w3wp.exe on IIS6/7) which exposes x86 and Script and attach as Script.