Backup Exec 2014 Error V-79-57344-4611 when backing up a VM seems to refer to the GRT feature. Bearing in mind this product is no longer supported by Symantec, the best course of action to get your backups running again will be to disable the GRT option within the individual backup job. I’ll investigate this further, but for now, this appears to be the only option.
The implications of turning off GRT is that you will not longer be able to restore individual files from within the backup software. However, you will have a solid image backup that you can restore to a temporary location and then retrieve the files you need from there.
Finally, use this time to review and upgrade your backup systems!!