Can’t find device driver: 4mmdat

I uninsatlled Arcserve and installed Backupexec. After hours of frustration because BE wouldn’t run, I uninstalled it. Now, I can’t get the NT backup to work. It says it can’t find the device but it finds the tape drive. I have removed and re-installed the 4mmdat file to no avail. What’s next besides re-installing NT?