Note from Support -
Confirm that the tapes you are using originate from a trusted seller. We have had reports of some tapes obtained through marketplace vendors (ex: Amazon, Ebay, NewEgg) being damaged, used or non functional. We love the convenience of marketplace sellers for all sorts of products, but tape is a highly specialized field and nothing sucks more than spending over $100 on something that does not work. You are much safer using people with experience in that field. We sell tapes on MagStor.com and can verify their authenticity.
If error code 6 is present and ejecting the tape clears the 6 error code, the media is the likely culprit.
If you are certain your tape is functional, but still see error code 6 or 7, contact MagStor support.