Some times I get " Media Write error " on some policies and unfortunately NBU does'nt try to use another Tape , when ever NBU encounters a corrupted tape ,it stops right there and nothing happens .
Is there a way to force a policy to use another tape in this situation ?
There are defaults within NBU that is preventing selection of another tape after the 1st I/O error.
Only when the tape is FROZEN will NBU no longer retry the same tape.
Certain TapeAlert media errors will cause NBU to freeze the tape on 1st error. (There is a section in Admin Guide II with details.)
I/O (CRC) errors such as yours will only freeze the tape after 3 errors in 12 hours.
The screenshot shows that this was Attempt 2. (NBU Global setting of 2 tries in 12 hours) So, it seems that NBU tried the backup twice with the same tape. Only after next error (if within TIME_WINDOW of 12 hours) will NBU freeze the tape.
You can change these defaults with nbemmcmd TIME_WINDOW and/or MEDIA_ERROR_THRESHOLD settings - see this TN for details:
DOCUMENTATION: How Veritas NetBackup determines if a tape should be frozen or the status of a tape drive should be changed to down, and how to change this behavior
Try to find why you are getting those Media Write error, you are getting CRC error and looks like somewhere the hardware might be problomatic. If you are getting it regularly try to see system logs why you are getting these errors.