What is the admin database?
The "admin" database is a special NIS map which holds information on when a usercode expires and what university ID is associated with it (NIS is the system we use to share usernames and passwords around our machines). When this error appears, it means it couldn't find the username in this admin database.
This isn't a serious error and there's no need to worry about it. It's normally caused by either the map being updated at the time the "expire" program is run in the login script or by some other system problem. It won't affect the use of your code or the UNIX systems.