Xcode clang exit code of 254 error message; what does it mean?

I have tried to develop an iOS app on Xcode 4.3 and it has failed and quite with the message: clang exit code of 254.

This has happened twice with the exact same error message. When it happened the first time, I closed my project, then quit Xcode and opened it again. I thought that I needed to flush my settings and should start over again to make sure that the error did not happen again. But it did.

Can you tell me what this error message means and tell me what I need to do to keep it from happening again?

Thank you.