Can't Read Certain Floppy Disks

Some floppy disks, usually older ones, are able to be
read within Win. XP/2k but other ones, even new ones, are
not. Sometimes I will get errors that the disk is not
formatted and when I try to format it, it won't let me.
Other times there are I/O errors.

This occurs on multiple machines with the new OS's. I
found a registry editor on the MS knowledge base, Art.
No. 811839, that didn't work.

Can anyone help me with this issue?

Thanks