Has the media been written to?? If there is data on the tape that has not expired, the media will not be able to be moved to a different volume pool.
Run the following to see if the tape has a 'Time Assigned':
Unix:
/usr/openv/volmgr/bin/vmquery -m <tape_ID>
Windows:
\<install_path>\veritas\volmgr\bin\vmquery -m <tape_ID>
Thanks,
Bob