Debugging on iPhone not working

I'm using Xcode 3 for developing iPhone apps. I've been able to debug apps on my iPhone by setting the IDE to Device 2.2.1 Debug. Only recently has this feature stopped working -- when i go to debug my app on the device all i get on my iPhone is a black screen. Xcode shows that it is in debug mode and running the app but nothing is showing on the device. I have to stop debugging and directly use the device to launch and test my app but without debugging.

Any ideas why this is happening?

Type this is terminal(copy and paste will work):

ln -s /Developer/Platforms/iPhoneOS.platform/DeviceSupport/3.0\ \(7A341\) /Developer/Platforms/iPhoneOS.platform/DeviceSupport/3.0.1

If you have put program other than default then you will need to change it accordingly.