Handling Diskette Errors
Diskettes can go bad. Usually they start by developing "soft" errors, which are recoverable by retrying the operation several times. Eventually the soft errors turn to "hard" errors that can not be recovered.
How do you know when a diskette is starting to go bad? Your first clue will be an error message like "Disk error reading Drive x, Abort, Retry, or Ignore?" When you start to see that happen to a diskette, it's time to do something.
Try the diskette in another diskette drive to ensure that the diskette is the problem, not the drive.