It looks like that is the exact error. I searched the Phrase Manager and it is in
listignoreuser phrase variable. It's just missing the username
Code:
Sorry {1} is a moderator/admin and you are not allowed to ignore him or her.
Maybe there's a bug and the username is not passed to the phrase. But it shouldn't trigger this error in the first place.
Steve, what is the vB version are you using?