问题
I have tried to clean out all targets and caches, restart Xcode, reset the simulator, kill all simulator processes and also restart my laptop, but nothing works and the following error still shows:
Couldn't register com.yourcompany.myApp with the bootstrap server. Error: unknown error code. This generally means that another instance of this process was already running or is hung in the debugger.
回答1:
Many have had this kind of error like here. I restarted my Mac and this error did not reappear.
回答2:
If you are running a Universal app in the simulator, build for the other device after you get this error.
So, if you got the error for the iPad sim, build for the iPhone without hitting "Stop" or closing the iPad sim. That will build for the iPhone in this case, then once it's running, build for the iPad...or vice versa. This is a quick fix without restarting, but it seems to stop working after a while.
It's also sometimes related to some of the AppDelegate methods like applicationWillTerminate, applicationWillEnterForeground, etc. Check your appDelegate methods for any bugs.
来源：https://stackoverflow.com/questions/8027411/bootstrap-error-ios-5-0-simulator-in-xcode-4-2