I have a feeling it has to do with this – by resolving this issue below, I bet I resolved this one, too:
I granted a badge that had no badge group. Since there’s no default group for badges and no warning you HAVE to have one or it’ll crash a user’s badge (if assigned), this causes both the error in this thread and the one linked above.
I recommend adding a default group for all badges that just sort of hovers to prevent this (better than warning - people dont read warnings, ehehe)