Tapes marked read only on SCSI tape drive. (4042652)

A lot of Read Only errors on customer's backups on tape library.

Sample errors from the Binary Log are:

1. Error 2010/01/18 15:35:11 55 Media BACKUPSVR BACKUPSVR 3-0.2.0 (TANDBERG LTO-4 HH): had media error

With sub text:
TAPESCSI:01772 85 0 153511 Unexpected error writing to media
MEDWRITE:01772 183 1 153511 Device write data out: FAILED

2. Error 2010/01/18 15:35:11 55 Media BACKUPSVR Error transferring data to Mid 'BACKUPSVR 18 Jan 15:34-1', marked read only

With sub text:
DEVMGR :01772 273 0 153511 bHardwareError = TRUE

3. Severe Error 2010/01/18 15:35:15 55 Data Plugin BACKUPSVR Fatal error writing backed up data

When NetVault has problems writing to tape, it marks it as "Read Only". This is for the user's  benefit and prevents you finding out at a later date that the Backup didn't work when you wish to perform a Restore. 

These errors generally point to the following reasons: 

A] The media is getting too old or damaged. 
B] Read / Write Head within the Tape Library needs cleaning. 
C] Read / Write Head and / or other hardware damage.