BE 2014 Reports Backup Failure - Access Denied

V-79-57344-41488 - Due to one or more errors in \\Server.domain.lcl\System?State, this backup cannot...
V-79-57344-33928 - Access Denied. Cannot backup directory \ and its subdirectories.

Backed up 26 System State components
1 item was skipped.
Processed 28,039,071,618 bytes in  18 minutes and  41 seconds.
Throughput rate: 1431 MB/min
Compression Type: Software
Software compression ratio: 1.7:1

One of my clients is getting the above message when backing up two domain controllers.  As you can see from the summary log entry, one component of the System State seems to be causing the problem.  A consistency check is run before the backup, and it is successful.  A backup with Active Directory GRT turned off is also successful; although the failure happens when AD GRT is on.  This backup has been running for over a year with no problems.  The client upgraded from BE 2012 to BE 2014 with no problems.  Nothing changed of which I am aware when the failures started.  Just one day, the failure reports started out of the blue.

I need to find out what is causing the backup to report "failed" and specifically find the System State component involved.  Anyone have an idea how to go about doing that?

Dell T610 server
Windows 2008 Server Standard with SP 2
One Hyper-V guest VM on the server
Symantec Endpoint Protection 12.1 client installed (latest version)
BE 2014 fully patched
30 gb memory
Plenty of disk space