Today I encountered this strange error:
Couldn't register applicationXXX 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.
It happend after I accidentally re-run the application while XCode was still building the code. Normally it doesn’t cause any trouble but for some reason it did. To solve this issue, I tried restarting XCode, iMac but the problem remains. until I see this article: http://stackoverflow.com/questions/788277/iphone-strange-error-when-testing-on-simulator that suggested to restart simulator. So, since I am using device directly, I restarted the device.
And it fixed the problem! haha very strange but interesting at the same time.