How to remove write protection from usb flash-drive?

I don’t know about others, but the drive worked fine this morning when I uploaded files from an XP box

That after noon, on a Win7 machine - it won’t accept writes or delete.

Meanwhile, the other two have been merrily writing and deleting from all three machines (xp, vista and win7).  Not reasuring to have a functional drive suddenly “quit” functioning when you need it.   (In this case, I did not happen to actually “need” it.)