Converting projects to Visual Studio 2008 doesn't always go smoothly.

You might see it blow up with a COMException error

If your ASP.NET web application project is configured to use IIS (instead of the built-in web server), then you'll need to run VS as Administrator (thanks to Mikhail posting that workaround) This is because VS needs to look in IIS's metabase and it requires admin privileges to do that.

I'm also getting a very helpful "The operation could not be completed"

Trying to dig deeper, I ran a debug instance of VS (eg. opened up VS and then ran another instance of VS inside that) to see if there were any exceptions that might give a clue as to what was going wrong.

I now get a little bit more info: COMException 0x80020009 "Function evaluation disabled because a previous function evaluation timed out. You must continue execution to reenable function evaluation."

I spent some time trying to figure this out, but in the end gave up and just created a new project in 2008 and copied in the old files.