Force close before onCreate, activity class not found exception.

Question

I just started testing my app on android 1.5, and it doesn't want to run at all. I have a breakpoint in onCreate on my main activity, but I get a ClassNotFound exception even before reaching that. The class not found appears to be the class of my main activity. The exception happens in: ActivityThread.performLaunchActivity

It runs fine on 1.6 and later, so I assume I'm using something that isn't supported on 1.5. But how can I find out what it is? Any tips on how to debug this would be greatly appreciated.

Thanks.