Backup Lockup

I am running NTBackup on and NT 4.0 server. It is setup to run from a batch file automatically using the AT command. The problem I am having is that the backup job will run OK for a number of days. Usually about 3 or 4. Then on about the 5th day, the backup job seems to hang. I will come back to check the logs and all I can see is that the backup job hung during the verification phase. When I run Task Manager & try to terminate the backup job, nothing happens. The only solution I have found is to reboot the server. Other than buying a different backup program, and solutions?