Hmmm
if it was append only, and if the wrong media set was mounted, then the tape would eject and ask for an appendable media
Since this job is else overwrite, if the tape is past the OPP it should write.
If you do an inventory before the job runs, does the tape header appear in blue or black?
Are you sure that the tape is ejecting before the job starts, o rcould the tape be filling up and asking for another?
Any alerts or Event Viewer entries?