Download the attached script. On the DPM 2010 server, copy and paste the contents into PowerShell for DPM
DPM Server: (enter DPM servers name)
Library: (enter the name of your tape drive libary as labelled within DPM)
Tape Location: (enter the slot that contains the tape that needs to be forced as free, i.e slot-1)
If multiple tapes are needed by forced as free, rerun the script again and enter slot location as slot-2 and so on. Refresh DPM and the tapes should now be free.