I understand your frustration.
It has been my experience where I had a SanDisk USB stick that worked fine in one Win 7 pc be classified as unwritable in another Win 7 pc. Putting it back in the 1st pc and it was writable just like before. I got it to work in the 2nd pc my changing the Win 7 Sharing options for it to Read/Write and adding the Everyone user id to it. SOME write protect / Read Only problems are Windows 7 related. But I agree, not all of them seem to be.
