It looks like your "define lib" command is correct but here are some
things to check:

Is the DAT the only device that could be using lb0? (It may be lb1,
lb2, etc.)

Try issuing the "lsdev" command to determine if the lb0 is available
to ADSM.  If it is not, use SMIT to make it available.  Here's an
example of the command and output:

$ lsdev -C -s scsi -H
name   status    location    description

hdisk0 Available 00-08-00-00 Other SCSI Disk Driv
rmt0   Available 00-08-00-40 2.3 GB 8mm Tape Driv
hdisk1 Available 00-08-00-10 Other SCSI Disk Driv
hdisk2 Available 00-08-00-20 Other SCSI Disk Driv
cd0    Available 00-08-00-30 CD-ROM Drive
mt0    Available 00-08-00-40 N/A
hdisk3 Available 00-08-00-50 Other SCSI Disk Driv
$

I hope this helps.

Tom Hepner