I have an iOS project that I've put in Dropbox to work with a few friends. The issue is that it seems to get "corrupted", so that after some time (after someone else has accessed the Xcode project file), when I try to go and open it again I get a Base SDK Missing error. In the Project Settings, I discover that I'm missing the valid ARM6/ARM7 architecture for iOS apps—I can only choose from 32-bit or 64-bit Intel. My only other options are i386, various forms of PPC, and x86_64. I simply can't build for iOS anymore.
No one else that I'm working with seems to have this problem. It exists in both Xcode 3 and 4, so it's not an Xcode 4 issue either.
Is anyone else having this problem? Is there a fix?