Today i had try it, and everything worked, like there was no error.
I think the problem is @Nadeo that there is an error at the Master-Server that the masterserver can't handle the Starts, Stops and Restarts of the Relays.?
I had the same error few days ago for twl0 finals when trying to start relays from a different computer.
I tried on same computer using /join=127.0.0.1:port , it worked... then after it worked also from the other computer (without having made any change, using /join=ip.ip.ip.ip:port)
And at the next start of the master it worked directly from the remote one. I really don't understand what happened, btw you can try the same, perhaps that it will also work for you.