I can do
io-usb
Fsys.umass

which prints

Path=0 - QNX USB Storage
target=0 lun=0 Direct-Access(0) -                 2GB                      Rev: 2.00

and creates a /dev/usb . Next I do
Fatfsys

which prints

Fatfsys: mount (removable) "/dev/fd0" at "/dos/a"
Fatfsys: mount (removable) "/dev/hd0" at "/dos/c"

all I get is a file /dos/c and not a directory, which isn't my USB key. 
What am I doing wrong?