Problems with Symantec Backup Exec & Domino

I have a Domino Server (version 5.0.12) (Windows 2000 Server) that previously had Veritas Backup Exec 8.5 installed, along with the Notes/Domino agent and the backup was done on tape on that server.  Earlier this year, we purchased a centralized backup system and upgraded to Symanted Backup Exec 11d for Windows Servers and are using remote agents.  All of our servers backed up to one tape.  I have not been confident with this approach, as we continue to have backup failures, mostly on the Domino Server.  The consultants didn't feel we needed the Domino agent so we didn't purchase it.  It's been hit & miss for months.  At times, the backup works fine, I've verified the data, the individual mail files were being backed up and I've restored some of them.  Other times, it gets hung up in an endless loop on the Domino server and then I have to try to cancel the job, which takes hours.  I've tried stopping and restarting the services and usually end up rebooting the server because it still does not cancel.  

I upgraded Domino to version 6.5, verified the backup and it worked great for about 1.5 weeks.  Then it started failing again, like before.  It would get hung up, I tried to cancel it, and it would continue to hang.  I've recently discovered that our individual mail files (person.nsf) are not being backed up at all.  We have spent a lot of money having the consultants check the backup out and I don't feel we have a resolution - rebooting isn't a solution, plus we need a consistent backup.  Now the suggestion is to buy the agent.  I've read other posts that have similar problems.  Before we spend more money on this, is there something that is being missed here - or is it as simple as buying the Domino agent?  Why would it all the sudden not backup the individual mail files?  The backup software is installed on a Windows 2003 server.