Xcode does not compile anymore :(

Hello,
I just upgraded from unity 3.3 to 3.4, and Xcode to 4.2 supporting iOS5, and now the project generated via unity won't compile anymore on Xcode.

The error I receive is weird: "iPhone_target_Prefix.pch' has been modified since the precompiled header was built"

I use a couple of Prime31 plugins, I don't know if they disturb the process (since they do some postprocessing).

Any help?
Thanks, Pasko