If you have been using the drive with ADSM, I think you have to put the drive 
in question in manual mode. I ran into a similar problem.

***************************************************************
          Montana Higher Education Student Association
Gary K. Luther                                        406-444-0631
2500 Broadway                               Helena, MT 59601
www.mhesac.org                         gluther AT mhesac DOT org
****************************************************************
PERSONAL
www.initco.net/~aixapl2                  aixapl2 AT initco DOT net
****************************************************************

>>> Ann Courchaine <acourcha AT CSC DOT COM> 12/16 8:32 AM >>>
Hi all,
     Is there a way to manual mount a 3570 tape? I issued the following
find ./file -print | cpio -ocvB > /dev/rmt0    this worked for the 4mm
drive
find ./file -print | cpio -ocvB > /dev/rmt3    will not work (or any other
device name associated with the lsdev command)

ie lsdev -Cc tape  outour is:
rmt0 Available 00-00-0S-6,0  5.0 GB 8mm Tape Drive
rmt1 Defined   00-02-01-11,0 IBM 3490F Tape Drive and Medium Changer
rmt2 Defined   00-02-01-11,0 Other SCSI Tape Drive
rmt3 Available 00-01-01-1,0  IBM Magstar MP Tape Subsystem
rmt4 Available 00-01-01-2,0  IBM Magstar MP Tape Subsystem
mt0  Available 00-01-01-1,0  ADSM Tape Drive
mt1  Available 00-01-01-2,0  ADSM Tape Drive