(Backup Exec) Constantly getting error E00084c8 and E0008703 on tests!

I am new at the company I work for and have been tasked with taking over as System Admin from the previous "consultant" <---air quotes there. They had Backup Exec running default build and it was erroring out constantly. I modified the maximum size for backup-to disk to 10 gb and the maximum number of back sets per backup to disk file to 200. All was well for about a month. Backups were completing a full 2 hours quicker than they were previously erroring at. All of the sudden I start getting e00084c8 errors. Now I am going through the event logs and I find that there are issues with a bad block in the raid. Which would be fine if I wasn't running windows server 2003 r2 with 2 terabytes of data. So I understand that I need to run a chkdsk which will take my DC down for a good couple hours in order to address the bad block. What makes things even worse is that the software is "owned" by the previous consultant who opted not to keep it up to date or extend the support contract. I am running 12.5 and I feel like punching a hole in Symantec's digi-face like I have so many times with Norton (thank god for norton removal tool). I am trying to make the evolutionary step to unitrends but I do not have the budget until next quarter. I am trying to backup about 700gigs through usb to "tape drive"(really it is a 2.5" sata drive in a cart... it appears to be solid state?) "Tapes" are 750 gigs. Any tips are appreciated.