Symantec Backup Exec 2012 cannot find tape drive slots

I have just upgraded to Symantec Backup Exec 2012 on Windows Server 2008 with a Dell 124t Autoloader.

The tape drive can be seen by Windows Device manager and Backup Executive, but it cannot see any of the slots. There are tapes loaded within the machine, and I have tried cycling power, updating the driver, stopping and restarting BE services.

I used to use a Version 10d on Windows Server 2003 with no issues.

Any ideas on what could be wrong?