Hi Ann,

  1. Check that no other application is trying to use these drives.
  2. Verify that they are powered on and online.
  3. Run a 'cfgmgr' from aix to make sure they come back available.  You can
also try deleting their defintions from smitty- devices-adsm-tapes, and then
adding them back in.
  4. Check your 'errpt -a | more' to make sure you don't have hw errors.
  5. Check the cabeling to make sure no cabels or terminators have come loose.

  Regards,  Tricia Jiang