Event ID-7 is a "Bad Block" on the Tape being using. By design, when a Bad Block is encounter, the Tape Drive "Seizes the Tape" and goes offline. It can sometimes be difficult to get the Tape Drive to release the Tape. Refer to the Users Manual for instrcutions on how to Reset the Tape Drive. Sometimes applying the Firmware Update willl reset the Tape Drive and Eject the Tape.
Do not assume the Tape is Bad, but do not re-use until tested. The Tape may be Bad, the Tape Drive may simply need Cleaning or the Tape Drive may be Worn or Damaged. If you are using 3rd Party Backup Software, such as Backup Exec or Yosemite, you wan want to check the Removable Storage Servcie to see if it is set to Manual or Automatic. Any Tape Devices would need to be first Deleted in the Library Section of Removable Storage, then Sop and Disable Removable Storage. Since Removable Storage is in effect NTBACKUP, this Service can interfere with the Operation of your Backup Software and generate "Bad Block" Errors.
To Test the Tape with your Quantum Tape Drive, use a tool called XTALK ( xTalk-188.8.131.52_Quantum_Setup.exe ) that is found on Quantums Website http://www.quantum.com/ServiceandSupport/Index.aspx
You may run a write_read_full Test on the Tape. Be sure to Clean the Tape Drive first. If it fails the Tape, try it with a 2nd Tape, If it fails again, suspect the Tape Drive.