Vista - ReadyBoost Flash Drive Snag

I put a Gizmo!JR 4GB USB2 flash drive in a spare USB2 socket and used the
proffered ReadyBoost tab to devote the whole of its capacity to ReadyBoost.
At some stage it stopped working (maybe because I "safely removed" it in
error instead of something else?) and now when I insert it I can see it as
Drive F, but when I try to do anything, like open it or reformat it, I am
asked to insert a disk into removable Drive F. When I look at its properties
the space is fully used. That is to say Used Space 0 Free Space 0 Capacity 0
and somewhere the usual message "The device is working properly" when it
isn't.

Is there any way I can use the drive again? Or is it a write-off?

Doug