can' seem to mount a usb memory stick

[Henry <nbsd4ever%gmail.com@localhost>]

Hi and TIA for help,

When I plugged the usb stick in, it seemed to be recognized correctly
as sd0.  I tried to mount it with:
# mount -t msdos /dev/sd0a /mnt
but got the error:
mount_msdos: /dev/sd0a on /mnt: Device not configured

What am I doing wrong?

Henry