[Q] A floppy will work fine, then all of a sudden I get missing sector (not bad
sector) errors, and I take the floppy out and put it back in and I can't even
FORMAT the thing. It was a brand new floppy, BTW.

[A] I recently ran into the same problem, 2 disk in a row. It was some
inexpensive, unbranded diskettes. My symptoms were nearly identical to yours,
including the inability to reformat the disks on the Aero, however, I could
reformat them on each an every (other) computer I tried!

[A] I've found that this problem tends to appear when you have smartdrive
running and fail to include "a-" in the command line. Even when drives
supposedly support floppy change detection, I've just never had good luck with
smartdrive & floppies. (By default, it read-caches them.) Try running "smartdrv
a-" and see what happens.

[A] I'll second at least some of this floppy trouble. When running dos or
windows I had a heck of a time getting floppys formatted. I finally got to the
point where I'd never bother trying to format disks on my Aero but use some
other machine. After getting them formatted (elsewhere) I had no troubles with
the disks. I haven't had this problem since I switched to Linux.

[A] I haven't had any trouble, and I have formatted about 30 disks of about 3
different varieties. Maybe there is a change in floppy supplier or model
somewhere, or maybe I've just been lucky.