Why is the VS 2010 debugger popping up when I'm trying to debug a VS 2008 app?

Question

I'm trying to debug an ASP.NET 3.5 app, which I've recently migrated from VS 2005. (This uses Crystal Reports 11 Release 2, but I don't know if that comes into what's causing me problems, or not.) This app uses Active Directory for authentication. I'll have the app opened in VS 2008, and then press the F5 key to start debugging. Shortly after that VS 2010's Just-In-Time debugger pops up and asked me if I want to (a) debug w3wp.exe, of (b) cancel debugging.

Huh? Why is VS 2010 coming up at all? I don't have it running. I'm not in it. I didn't press F5 in VS 2010. I am in VS 2008 and press Run/Debug there. What's going on; why is VS 2010 interferring?

Answer 1

Edit: Sorry I had to edit my answer. It turned out to be a little more complicated when two versions of VS are involved. Hopefully this edit is more accurate.

If you go to Tools > Options > Debugging > Just-in Time you can enable/disable JIT debugging for the specific version of VS. If you enable more than one VS as JIT debugger, you get to pick between them or set one of them as a default when the VS Jit Debugger is launched. I assume VS2010 replaced your VS2008 JIT debugger during install, so to re-enable it you need to launch VS2008 and go to the menu and enable it. I had to disable and then enable it to get it to work.

If you have set some other debugger, e.g. WinDbg as your JIT debugger, it is a matter of changing the following registry key HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\AeDebug\Debugger to point to the desired debugger. Please note that if you run 64 bit Windows there's a shadow entry as well in the Wow64 section. This guide has additional details.