I just upgraded to Xcode 4 and for some reason my app won't run in the simulator or iOS device. It was working perfectly in Xcode 3, but all of a sudden now when I press run the program stops at "Attaching to...". There doesn't seem to be any other info to help with this problem either.
For summary you can try following things to tackle the issue:
Fixed it!! Hopefully this helps some people avoid a very frustrating couple hours. I solved this by:
Hope this helps!