Backup Lockup

I have an NT 4 server as a PDC for a small office. We are running backups using a batch file and the AT command. The backups will run OK for a couple of days. Then about the 3rd day, the backup will not complete 100%. It appears to run the backup and verify. But the backup job is left hanging, as if it might be waiting for something to happen. I am unable to quit the backup job using Task Manager. The only way out is to reboot the server.

Anyone have any insight on this problem?

Thanks.
J Roberts