Bakunin,
Thanks for the advice. Unfortunately, the usernames are set to a standardized format, so length is not an issue. Also, we don't see this issue on our 6.1.5 servers, just the servers at 6100-07-04-1216.
My colleagues think it's an issue with a PAM module working with ssh. We thought we had a fix but it may not have taken (don't have details on the fix at this time). It's not breaking anything but seeing a false message like that is... well...
Mike