The error mentioned in Description1 is resolved in Backup Exec 2010 R3 Hotfix 159965
The error mentioned in Description2 is resolved in Backup Exec 2012 Hotfix 180962
 
Workarounds :
1.  Backup the affected AVVI systems to a B2D with, or without GRT enabled.
or
2.  Backup the affected AVVI system to the deduplication folder with GRT disabled.
or
3.  Disable the AVVI Deduplication Stream Handler.

Note: Incorrect use of the Windows Registry Editor can have disastrous results on a server Operating System. Great care should be taken when making changes to a Windows Registry. Registry modifications should only be carried-out by persons experienced in the use of the Registry Editor application.
 
Note: Disabling the AVVI Deduplication Stream Handler will result in lower deduplication rates for AVVI backups performed on this media server.  It is recommended to subscribe to this technote in order to get a notification when this issues has been resolved.  After that point, it is recommended to delete this registry key to re-enable the AVVI Deduplication Stream Handler.
 
Note: As long as the AVVI Deduplication Stream Handler is disabled in this manner, Backup Exec will not be able to restore backups that were done while the Stream Handler was still enabled.  It is necessary to re-enable the Stream Handler in order to restore from these backups.
 
Using regedit, create the  HKEY_LOCAL_MACHINE\Software\Symantec\Backup Exec For Windows\Backup Exec\Engine\VMware Agent registry key.
Then, create a DWORD value in this key named "Disable NTFS File Extent Mapping" and give it a value of 1.
 
In order to verify that the key has been created properly, turn on debug logging for BEREMOTE and run an AVVI backup to a deduplication folder.  The string "VM_VCBPROXY_FS::GenerateDiskDetailsForVM" should NOT be seen in the SGMON log associated with this job.