It looks as if Visual Studio is confused. The event you mentioned, does exist in the code. What you can do is try restarting Visual Studio and running. If that does not help, try cleaning out the temporary asp.net websites folder located at
Quote:
C:\Windows\Microsoft.NET\Framework\{version}\Temporary ASP.NET Files
I know it sounds stupid but sometimes it does work perfectly. If you have windows installed in different directory, then make sure that you replace the drive letter. And also replace the {version} placeholder with the framework version you are developing. You can just browse to that directory and do it :)
Do let me know if this helps. If not, I will modify the answer accordingly.