Sony VAIO computer - Manual (Page 190)

Why is the drive unable to write data to a floppy disk?
Make sure the floppy disk is properly inserted in the drive. See Inserting and removing floppy disks for instructions on how
to insert the disk properly.
If the disk is inserted properly and you are still unable to write data to it, the disk may be full or write-protected. You can
either use a floppy disk that is not write-protected or disable the write-protect feature.
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