Application Error in Application event view log on media server

Hello,

We are running Netback 7.5.0.6 on windows server 2008 sp1 R2.

All our media servers with the same version as the master, 7.5.0.6.

Yesterday on the Backup window many backups failed at the same time on the same media server.

I tried to find what was the reason and found the following error in the event log in the media server:

please advise.