When you enter the serial number for AOFO does it get added under the Existing serial number?
If yes, then it should automatically make the AOFO option selected, " idealy speaking".
Incase it still shows res x. Then try these steps:
Note:First Remove the AOFO serial number .
1) Repair Backupexec:
Repairing VERITAS Backup Exec (tm) 9.x for Windows Servers
http://support.veritas.com/docs/253199
2) Once repair is done, Go to tools--serial number and installation ----insert the AOFO license number and check oout the result.