I got this error message recently on a project that worked fine when I tried last (WordPress for iOS). The error didn’t make any sense, and no matter what I tried the app wouldn’t compile anymore, always stopping with the following error message:

/Applications/Xcode.app/Contents/Developer/Platforms/iPhoneSimulator.platform/Developer/usr/bin/ibtool failed with exit code 255

I can imagine Xcode gets confused at times, as I currently have Xcode 4.6.3 and Xcode 5.0 installed, and I use them both (though not at the same time).

A quick Google search reveals a few possibilities to clear this up:

• clean the app (Product – Clean)
• restart Xcode
• reboot your system

The latter point worked for me. Threads dealing with the same problem:

• https://discussions.apple.com/thread/3178402?start=0&tstart=0
• http://stackoverflow.com/questions/15422033/all-of-a-sudden-app-wont-build