As far as I can tell, if you get this error when trying to run your app in the iOS simulator:

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Couldn't register com.greenpointware.Konk-iOS 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.

the only course of action is to restart your machine. I’m sure there’s a process hung in the background that’s preventing it from working, as this line from the internets seems to suggest:

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kill -9 `ps ax | grep Simulator | grep -v grep | awk '{print $1}'`

but that didn’t work for me. Rebooting did.