This is an Informational Thread that may help anyone else who encounters the same Issue I did.
The setup was backup to Disk, backing up to a remote Windows 2008 R2 box.
Backups would fail after 4GB had been copied (Size of one .bkf file)
The job would fail with the following status
Final error: 0xe00084f4 - An unknown error has occurred.
Final error category: System Errors
For additional information regarding this error refer to link V-79-57344-34036
and the following error
This turned out to be a mismatch between the write cache status in Backup exec and on the RAID card of the Backup location
Storage device "Remote Backup Location" reported an error on a request to write data to media.
The process cannot access the file because it is being used by another process.
V-79-57344-34036 - An unknown error has occurred.
Backup Exec was set to auto, and was assuming write cache was enabled.
The Backup location had write cache disabled.
Enabling Write cache on the remote Backup location fixed the issue.
Hope this is helpful for anyone else who encounters the same error
(MOD note - wasn't certain if this was the correct forum for Backup software posts - please feel free to move if required)