After migrating from SBS 2003 to Server 2008 R2, and upgrading Backup Exec from 12.5 to 2010 R3, I received an email stating backup had failed. [more] 

The error wasn’t too helpful and stated: “Final Error: 0xe00084af - The directory or file was not found, or could not be accessed.” and “Directory C:\WINDOWS\SYSVOL\sysvol\\DO_NOT_REMOVE_NtFrs_PreInstall_Directory was not found, or could not be accessed.” 

After some searching through the Symantec KB, I stumbled upon this article -- -- which stated that this error may occur when conducting a volume-level backup of the system drive after applying Backup Exec 2010 R3 Service Pack 3. There wasn’t a fix for the problem, but their was a workaround which stated "Create a new backup job by selecting the server from “Favorite Resources” or “User-defined Selections” "

Sure enough, selecting the resources so that it would back up via file://servername/c$ instead of C: allowed it to function correctly.