Hello Martin, How many cable do you have coming from the back of the tape drive?  If you connected a SAS cable to both ports on the back of the drive then that is your issue as you only need on port on the drive to be cabled at a time.   Please let us know if you have any other questions.
Just installed a new TL2000 on a Dell R630 server. Using 6Gbps SAS HBA. Windows 2008 R2. In Device Manager I can see two "unknown medium changer" and two tape drives (IBM ULT3580-HH4). However in reality there is only one library and one drive.  Windows has allocated a different SCSI id to each "drive" and "changer". Does anyone know why Windows is detecting two devices when there is only one? (see attachment screen shot)
PowerVault TL2000 library - tape drive appearing twice in Device Manager