Check logs by "bperror -all -hoursago XX " or so on.
You can find some relating messages like below.
FREEZING media id %s, Encryption unavailable for an ENCR pool
FREEZING media id %s, External event caused rewind during write, all data on media is lost
FREEZING media id %s, Medium identifiers do not match
FREEZING media id %s, Operation requested via BPTM
FREEZING media id %s, WORM media detected in a non-WORM pool
FREEZING media id %s, it contains %s data and cannot be used for backups
FREEZING media id %s, it didn't convert to WORM and cannot be used for backups
FREEZING media id %s, it is cleaning media and cannot be used for backups
FREEZING media id %s, it is unmountable and cannot be used for backups
FREEZING media id %s, it is write protected and cannot be used for backups
FREEZING media id %s, its a WORM platter thats already been written to
FREEZING media id %s, non-WORM media detected in a WORM pool
FREEZING media id %s, third party copy block miscompare
FREEZING media id %s, too many data blocks written, check tape/driver block size configuration
FROZE media id %s, could not write tape mark to begin new image
FROZE media id %s, could not locate correct position to begin new image
FROZE media id %s, could not locate correct position to begin new image
FROZE media id %s, could not locate correct position on optical disk
FROZE media id %s, could not write backup header to begin new image
FROZE media id %s, could not write tape mark to begin new image
FREEZING media id %s, it contains %s data and cannot be used for backups is logged when the tape contains some data that should not be overwritten, like TAR, Offline Catalog Backup(NetBackup database backup), ...
If you doesn"\'t need these data, label volumes without "Veriry ..." checked.