journal <str> backup (sequence <num>) already active

  Explanation:  An AIJ backup is already active for the specified
  journal.  In most cases, the previously active backup is being
  performed by the background AIJ backup server.  This problem
  only occurs when using the "by-sequence" AIJ backup option, and
  normally when specifying only a single AIJ sequence number value
  (i.e.  "/SEQUENCE=15").

  User Action:  Let the active backup finish before attempting to
  start another AIJ backup operation, or specify both a starting
  and ending AIJ sequence number (i.e.  "/SEQUENCE=(15,15)").