I've checked the forum code (remember, it's not our product), this message appears only in Instant Message handling and is kind of fatal error message.
It does database query using your name, the other name etc. and if such query returns less than 1 records, it displays the above message.
I think it could occur in two cases:
a) you delete the IM and then you try to do it in other window
b) you do reload, or click twice on the same IM.
Forget it, I think. Just a bit of bad wording.