Xcode 5.1 Error spawning child process: Permission denied
I had the same problem and after some Product -> Clean the message disappeared. So you should try that way!
I've had to do a clean build of the project and restart both the Xcode 5.1 and the iOS Simulator to solve the problem.
I had the same error. I removed a few lines of commented code, and cleaned the build, before compiling it again. Sounds crazy, but it worked.
Are you having any LLDB errors along with the "Error spawning child process" one?