Media Freezing

Hi Guys,

Recently i have encountered a problem while backing up of data.

The following error was observed in the detailed status of the job:

Error bptm (pid:3876) FREEZING media id <media id>, Externl event caused rewind during write, all data on the media is lost

Could someone pls explain me the reason for the below error, and will the previous data is all lost and if so how can i recover it.

thanks