This error is caused by the 'nobody' user somehow being set as monitoring one or more items in TeamForge.
You can see if this is the case with your TeamForge install by running the following against your TeamForge database:
select count(*) from mntr_subscription where user_id=`user1002`;
If the above returns a count greater than zero, then this is the problem. To correct this, do the following:
Note: You should make a backup of your database before attempting this procedure.