This error means that there was a crash while executing one of Client Commands. It could be an admin client command or just regular reborn client command. Anyway, it would be really helpful if they used developer 2 so we could know what was executed or something.
Ahh well a trusted admin was using commands when the server crashed as they were checking who was on from the previous crash and I did not see that exception code in their other server crashes so think this was just as you said.