NT 4.0 Scheduled tasks do not start

I have an NT 4.0 server with SP6. The tape backup drive failed and I installed a new one a couple of months ago. We’re using NTBackup, which works fine manually, but I cannot get it to start automatically. The batch file works fine when called manually as well (tapebackup.bat). But the AT command doesn’t seem to do anything – not even an error message. The Schedule service seems to be started because when I start it, it says it’s already started. I can stop and start that service, but I don’t remember seeing it in the services list from Control Panel. When I type AT at the command prompt, the task looks correct (only one task scheduled). Any ideas?

Thanks,
Jon