Log message referring to Gatekeeper appears occasionally when running simulator
I agree with the other respondents that this is a bug.
In the mean time, a work-around is to quit the iOS Simulator and restart it. I've had to do this as I alternate testing between different devices.
Can you try the beta of Xcode 4.5 to see if this behavior exists ... If it does, I suggest filing Radars : https://bugreport.apple.com
The new os mountain lion has a feature called Gatekeeper that the service is trying to run through. What i have heard is that there are lots of bugs with Xcode and the new OS. My guess is that it is a bug and will probably be resolved once apple comes out with an update and many bug fixes.