Hi,
The "Physical Volume Library Media not found" issue could occur if in the backup job properties, "Append to media, terminate job if no appendable media is available" is specified and there is no space to append. Hence, the backup job is getting terminated.
Refer to the following technote for more information:
http://seer.support.veritas.com/docs/192180.htm
To check whether the media is appendable, run the changer inventory report and look for the values described in the following technote:
http://seer.support.veritas.com/docs/192180.htm
You may also refer to the following technote:
When running a job to a Backup-to-Disk folder, an alert appears stating: "The Backup-to-Disk folder is offline."
http://seer.support.veritas.com/docs/236295.htm