VM backup job completes with exception V-79-57344-38721 - Failed to mount one or more virtual disk images.

Problem
 

VM backup job completes with exception V-79-57344-38721 - Failed to mount one or more virtual disk images.

Error Message

V-79-57344-38721 - Failed to mount one or more virtual disk images.
 

Cause

1. Antivirus exclusions are not configured on the Backup Exec server, Hyper-V Host and the VM being backed up.

2. Virtfile driver is not installed. Running the command sc query virtfile provides the following output:

3. Virtfile driver version is not current and in which case it will need to be updated or reinstalled.

Solution

1. Configure Antivirus exclusions on Backup Exec server, Hyper-V host and VM machine as per the following article:
List of Anti-virus exclusions to configure for Backup Exec

2. If Virtfile driver is missing, install the Virtfile driver by navigating to C:\Program Files\Veritas\Backup Exec\Virtfile and installing the Virtfile.inf file (Right Click on the file --> Install).

Once the Virtfile driver is installed, run the command sc query virtfile to make sure that the Virtfile driver is visible. Reboot the server to make ensure that the Virtfile driver is loaded and running by running sc query virtfile command.

3. Update Remote agent on Hyper-V host. Ensure that the Virtfile driver version is same on all machines - Backup Exec Server, Hyper-V host and Virtual machine.

Remote Server path - C:\Program Files\Veritas\Backup Exec\RAWS\VirtFile\
BE Server path - C:\Program Files\Veritas\Backup Exec\VirtFile\
Ensure to match the virtfile driver version at following location on all servers -> C:\Windows\System32\drivers 

If the Issue is still not solved please contact Backup Exec Technical Support for further assistance.