By default Edit and Continue (EnC) is disabled when you create a new ASP.NET Web Application using Visual Studio 2005. Not sure why this is because EnC is a really nice feature to have and can be a big time saver.
You will notice this when you try to edit the source while debugging and receive the following error message:
Edit and Continue
Changes are not allowed when the debugger has been attached to an already running process or the code being debugged was optimized at build or run time.
Fixing it is easy. Just double click on “My Project”, select the Web tab and check the “Enable Edit and Continue” check. Next time when you run you are all set for EnC [:)]