The virtual path maps to another application, which is not allowed

This problem comes when you copy a complete asp.net website to new folder/location/computer. And "Virtual Path" (same path which you see in browser address bar alongwith localhost and port number) in property is set to the folder name where complete site was originally placed. This can be resolved by removing folder name from virtual path.

Go to website in solution explorer.

Click F4, website properties will open.

Remove folder name from virtual path.