Your Anti-virus active-scan may be messing with your file . IMHO always have your Anti-virus ASK what to do (At least you will know it was doing something to a file)
You have a (marginal) defective USB port on either your device or your PC (they don't play nice together)
(My first PEz would fail (and corrupt the file system) if I used a Intel 82801 based USB port in USB2 mode. My Second PEz works just peachy on the same Intel port.)