Make darn sure your drive element numbers and SCSI ids are square.  What I mean 
is if you are incorrectly assigning an element number to a drive, say SCSI ID 
0, which should have element id 32, but you've set it to 36.  I've seen what 
you have described happen when this has been done.

There is a utility called lbtest.  I'm not exactly sure where it will be on 
your AIX system, but find it.  Then use it by issueing:

lbtest -d /dev/lb0 (or whatever your library device is)

Then select manual test, open library (selection 6), then return element count 
(selection 8, me thinks) and then return library inventory (selection 9).  This 
will scroll by fast, but at the top you will find the drives.  The element 
number and then scsi ID are shown there and you can verify you've got this 
correct in ADSM.

Hope some of this helps.  Let us know!

Thanks,

Kelly Lipp
SSSI