its having a file open error, try again, it will work eventually, make sure u have the filename typed in correctly.
In DOS hit dir/p and go down to the filename and find the bin file thats ur new bios. Type it exactly like u see it even if it says .... ATIX850~~.bin
Also an easier way to do this is to rename the file something easy that u can remember . I dont remember if ive done this before but i think it works too. Try something like MyFruityMEMBER.bin...lol jk
Somtimes typing it the way u see it in windows isnt the correct way to load it in DOS.
Other problems also is that the floppy drive that ur using could just be crap.
hope this helps.