There's nothing in your `mt status` that says what tape drive it's talking
to. My guess is that your SCSI devices got renumbered somehow. I think the
nst* devices are issued in the order they're found, and if the device that
was nst0 is gone, nst1 is now nst0.

Try `mt -f /dev/nst0 status` and `mt -f /dev/nst1 status` and see which one
looks like your tape drive.

Could there still be an issue with tape numbering, even with this behavior?

Thanks a lot!