Xcode Bot Failing after upgrading to Xcode 5.1
It turns out, that in automatically updating Xcode to 5.1 it uninstalls the iOS 7.0 simulator and replaces it with the iOS 7.1 simulator. It doesn't think to update the build settings on the Xcode server.
So to fix the problem, you have to manually open Xcode on your server, it then prompts you to install several items which you need to do. Then go to xcode preferences > Downloads and you can reinstall the iOS 7.0 simulator.
Really logical, thanks Apple...
I had the same error popping up on my Xcode build server (mac mini running OS X Yosemite and building using Xcode 6.1.1). The build was failing because of that.
It turned out I had an iPhone plugged in to the mac mini that "did not trust" the mac it was connected to!
Solution: plugged it out, restarted the integration, SUCCESS!
You'd think such an elaborate system should be smarter about trivial issues like this...