STATUS CODE: 91, occurs when trying to move media from one volume pool to another.

Overview:
Symantec NetBackup (tm) will not allow a tape with active images to be moved from one volume pool to another if the tape is already assigned.  Attempting to change the volume pool for an assigned media will result in the error "Change pool of <mediaid> failed(91)".

Troubleshooting:
The vmquery command can be used to determine if the tape is assigned or not.  Check the "assigned:" entry to see if an assigned time has been set.  If an assigned time has been set, the tape cannot be moved to another volume pool until all valid images have expired.  The following example is from a Solaris 9 master server, which has an assigned time for media ID A00001.

# /usr/openv/volmgr/bin/vmquery -m A00001
===================================================
media ID:              A00001
media type:            DLT cartridge tape (11)
barcode:               --------
media description:     ------
volume pool:           NetBackup (1)
...
created:               Thu Aug 25 13:22:21 CDT 2005
assigned:              Wed Dec  7 21:02:14 CST 2005
...
status:                0x0
===================================================

The bpmedialist command can then be used to determine if there are valid images still on the tape.  If there are valid images still on the tape, then the tape cannot be moved to another volume pool until all valid images have expired.  The following example shows 80 valid images still remain on media ID A00001.

# /usr/openv/netbackup/bin/admincmd/bpmedialist -m A00001
Server Host = beamer

id     rl  images   allocated        last updated <snip>
          vimages   expiration       last read    <snip>
---------------------------------------------------<snip>
A00001   2    174   12/07/2005 21:02  01/08/2006   <snip>
              80   01/29/2006 21:06        N/A       

The bpimmedia command can be used to display any IMAGE or FRAG lines that reference the tape.   The bpimmedia command will display a set of IMAGE and FRAG lines for each valid image.
# /usr/openv/netbackup/bin/admincmd/bpimmedia -mediaid A00001  |more
IMAGE hostname 7 hostname_1136776013 <snip>
FRAG 1 -1 3825 0 2 13 174 A00001 <snip>
FRAG 1 1 148800 0 2 13 172 A00001 <snip>
FRAG 1 2 12757 0 2 13 173 A00001 <snip>
<<--remaining entries-->>

Log Files:  n/a

Resolution:
Under normal operation, it is necessary to wait for all valid images to expire before attempting to move a tape from one volume pool to another.  NetBackup will deassign the tape once all valid images have been expired.  Once the tape has been deassigned, the tape can be moved to a new volume pool.

In situations where the tape is listed with an assigned date, but where NO valid images exist on the tape, the following command can be run:  
# bpexpdate -deassignempty -m <mediaid>

This will clear the assigned time on the tape and allow it to be moved to another pool.  Note: This command will fail when there are still valid images on the tape. Normally, it is not necessary to run this command to deassign a tape.  NetBackup should clear the assigned time automatically once the last image on a tape expires.  Once all the images are expired the tape can be moved to a new volume pool.  

Additionally, if a media has valid images, but that images are no longer desired, the following command may be run:
# bpexpdate -m <mediaid> -d 0
Warning:  This command will erase all NetBackup catalog information for the media for which it is run.