Upgrading to xcode 4 error No architectures to compile for

Question

I am getting an error after upgrading to xcode 4, for all of the library projects that my application depends on.

[BEROR]No architectures to compile f

Answer 1

Open project.pbxproj (show package content of xcodeproj file), remove all lines with VALID_ARCHS = "...";, and restart Xcode.