exabyte vxa-2 tape drive error

I am getting an error while backing up to my Exabyte VXA-2 tape
drive on certain tapes. This is the second tape for this occurance.
I own 10 tapes (I have written to each tape several times now).
The error message is:

Error: TapeAlert: Your data is at risk:
1. Copy any data you require from this tape.
2. Do not use this tape again.
3. Restart the operation with a different tape.

TapeAlert: The tape is from a faulty batch or the tape drive is faulty:
1. Use a good tape to test the drive.
2. If the problem persists, call the tape drive supplier helpline.
Error: An error occurred while writing the backup data.
A defective or damaged area was detected on the media.

Please:
1. Make sure your media and device are clean and free of all debris.
2. Verify the device connections and the device settings.
3. If the media is severely damaged, please discard the media after all data possible has been restored.
4. Please use another media or try using the erase or format menu item to repair the media.
(08-03-23-13-0406)

Operation Completed - No ( Cancelled )
Backup Job Ended - 9/15/2003 9:07:46AM

I am using Windows XP Pro. I am using Veritas Backup Exec Pro
version 4.61. I am backing up 10 PCs to my tape for a total of a
about 100 GB written to the tape. I have to all of my tapes several
times now. I do own a cleaning tape and run it when I am told to
by the software.

Do you know why this error is occuring ?

Sincerely,
Lynn McGuire