Back when floppy drives cost $500, they had some semblance of quality.

Now that they're $11 at Fry's (that's $5 before markup, $1 before shipping 
from Japan, and $.13 of materials) they are almost without fail ... prone 
to fail.

You might try using brand-new formatted disks.  Be sure if you put a 
floppy into a Windows box that you write-protect it, since Windows writes 
on a disk even if you only do a directory!  (It's updating the "Last 
Access Time."  Rah.)  Thus merely reading a disk on someone else's machine 
with a misaligned drive can trash the disk.

\\/
http://www.wlindley.com