Try running a floppy drive cleaning disk! Or if you don't have access to one some good old Q-Tips and rubbing alcohol should also do the trick.
I have a Mega4 STE which was constantly giving me read/write errors & bomb outs when accessing the floppy or reformatting it. The cleaning seems to have fixed everything!
3.5" Floppy Drive Cleaners are getting harder and harder to come by as 3.5" drives become increasingly passe'. Try RadioShack... I think even carry 5.25" floppies to this day! :-)
