MS Exchange error when backing up in Symantec

Hello:

I have been running a backup job in Symantec Backup Exec 2010 for MS Exchange server 2010 for a long time with no errors but the last 3 backups have failed with the following error:

v-79-57344-759 Unable to complete the operation for the selected resource using the specified options for the following reason:  VFF Open Failure.  This can be caused by low memory or disk resources.

The server does not have low memory or disk resources.  So I checked the event log at the time of failure and found this:
Event ID: 8  Source MSExchange CmdletLogs  The log is very long and way over my head but it starts with Task Get-User throwing unhandled exception.  System.Management.Automation.PiplineStoppedException:  the pipline has been stopped.

I am rather new to Exchange management so I really could use some help.

I have Exchange on a Windows 2008 r2 server.

Please let me know how I can track down and resolve the issue.

Thank you in advance