Emax

Hi,
Im trying to download the plus os to upgrade the base emaxHD to use 
with scsi. ( i think i can after opening it up)
ive downloaded program  here's what happens:
I select the write to disk command (under dos)
it asks for DOS filename which i enter emaxos.emx 
it then reads 'address mark not found hit any key to continue' and 
then it just goes back to main menu.
what am i doing wrong?
i have tried both the (w) command and the (p) command
i have also selected the (a) drive which i think is the floppy drive.
help im not familiar with DOS.