The discussion about 8" write enable tabs reminds me of a box of Imation
disks that I have here. I was asked to make a few copies for a customer
and was absolutely stymied when the target disks kept showing up as
write-protected.
It turned out that the Imation-provided tabs are made of a translucent
red-colored plastic with the appropriate sticky coating. Evidently, the
tabs aren't sufficiently opaque for the write-enable optical sensors on
my Siemens drives.
Replacing the tabs with ordinary foil tabs solved the problem.
--Chuck