Xcode 4 failed to launch

Long shot, but:

The Famous Web Editor

Xcode and the compiler can sometimes trip over spaces in the project/target name. This usually shows up in broken header or library search paths, so I'm not sure if it applies here. But it's certainly worth a try to rename the target so it contains no spaces.

First clear your DerivedData  (/Library/Developer/Xcode/DerivedData/) delete every thing from there.

Now restart your XCode, Restart your device.

run Xcode