I had the same problem with one out of my 1300 users. The problem was with the user account in the DLO console. I tried to delete the account and it just would not delete. A Symantec advanced DBA suggested I dump my database and start fresh. This would have rendered all backed up data (7 TB) useless because all recovery keys would not match. One user was not worth dumping all data across my global offices.
After several months, I actually fixed it this week. The DLO console had lots of PC's in the DB that did not have network storage folders. Any old PC's were deleted. Any user backups on PC's for any user who was not assigned to that machine was also deleted. After a major clean up, that one user that I could never delete, was magically deleted. Maybe I got lucky, but again support could not help me....!!!
