I dont freeze tapes - instead I am suspending (NBU is freezing tapes when finds issues with it).
I am suspending tapes before sending them to offsite location.
You know what is the difference between FROZEN and SUSPENDED tape?
"A frozen volume is unavailable for future backups. A frozen volume never expires, even after the retention period ends for all backups on the media. The media ID is never deleted from the NetBackup media catalog, and it remains assigned to NetBackup."
"You cannot use a suspended volume for backups until retention periods for all backups on it have expired. At that time, NetBackup deletes the suspended volume from the NetBackup media catalog and unassigns it from NetBackup.
A suspended volume is available for restores. If the backups have expired, you must import the backups first."

And here desc why NBU is freezing media (one of many)
"Repeated write failures are usually the cause for setting a volume to the FROZEN state or a device to DOWN. A volume is also set to FROZEN if the write failure makes future attempts at tape positioning unreliable. Common reasons for write failures are dirty write heads or old media."

All quoatation taken from admin guide for NBU vol 1.
Heer under You will find links to these docs

- System Administrator's Guide for UNIX and Linux, Volume 2 (  http://seer.entsupport.symantec.com/docs/290202.htm )

DOCUMENTATION: How Veritas NetBackup 6.x (tm) 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

I'd rather suspend media that freezing. But at times i find that tapes go into the frozen state; as soon as i pick-up the frozen tape state, i just run media unfreeze command to unfreeze/defrost tape.
Perhaps I just hate it when tapes are frozen... LOL

 frozen tapes 
frozen tapes = bad media or the tape drive is whacked

Mr fix it is sorta correct, use suspend if you dont want to use the tape.

then you know if you have a frozen tape then that means that there is something wrong with the tape or a tape drive.

that way it never gets too hot in the data center. :)

Is the image written on  frozen tape retained even though after expiration of image date .

Thanks,
Debashish

Frozen Volume-> A frozen volume is unavailable for future backups. A frozen volume never expires, even after the retention period ends for all backups on the media. The media ID is never deleted from the NetBackup media catalog, and it remains assigned to NetBackup.

Suspended Volume-> You cannot use a suspended volume for backups until retention periods for all backups on it have expired. At that time, NetBackup deletes the suspended volume from the NetBackup media catalog and unassigns it from NetBackup.
A suspended volume is available for restores. If the backups have expired, you must import the backups first.

Thanks & Regards
L.K.Nishad.

tapes only get frozen when.

1 tape is locked
2 tape is bad
3 tape was put in a bad drive

frozen is only used when you dont what to have anything use the tape, or there is a problem with the tape.