The Virtual Disk service terminated

Hello Experts,

We are facing a problem in our environments our windows administrator complained me that his virtual disk service is getting terminated whenever the backup start for that particular host , is this really a problem with Netbakup if well please give me the solution.
Client netbackup 7.7.3
OS:  windows 2008R2 (virtual).
Backup Type is Filesystem Backup of a Database server .

Thanks,