I got the same error - V-79-57344-65097 - Error. Cannot backup directory \zzzVirtApp009zzz and its subdirectories. when backing up Exchange 2007 situated at Windows 2008 R2 Hyper-V environment.
Virtual machine named "MAIL" is:
8Gb vitual ram, 4 ...
I have the same error - at the random time bengine.exe service stop with the same error in event viewer.
I'm using 2008 R2 with Dell PowerVault 132T (double drive) library. It's strange, but there were no errors while I testing BE2010 with Dell TL200...