Xcode version 4.6.2 (4H1003) compiler error

Do a Clean of the project; hold Option so that you are cleaning out the whole build folder and intermediates. You might have to quit Xcode and throw away the whole contents of the DerivedData folder by hand in the Finder, as I describe here: How to Empty Caches and Clean All Targets Xcode 4

Go to your project's Build Settings, find a setting named Precompiled Headers Cache Path, then delete that folder

Do a cleanup using command+shift+k and run existing project again.

From XCode 4.6.2 Release Notes

Known Issues

Building

When building a product previously built with Xcode 4.6.1 or earlier, the build fails with an error similar to this one:

PCH file built from a different branch ((clang-425.0.27)) than the compiler ((clang-425.0.28))

To address this issue, choose Product > Clean before building your product. 13663167

Performing Product > Clean works