Hello Lee,
Please go in the Device and Media Tab in the Backupexec and set the the Job to a particular Drive and not to 'all drives'.
You can also go through the Following Articles:
When performing a backup or restore in Backup Exec, the error message: "Unable to acquire device. The backup device this operation is attempting to use cannot be found. Please select another backup device for this operation" (a0008104 HEX or e0008104 HEX) is reported.
http://support.veritas.com/docs/238069
How to resolve hardware communication/detection issues with Backup Exec
http://support.veritas.com/docs/237047
---------------------------------------------------------------------
Let us know the result.
******************************************************************
*****************************************************************
Note : If we do not receive your reply within two business days, this post would be marked ‘assumed answered’ and would be moved to ‘answered questions’ pool.
Thanks.