Vista - ReadyBoost unready

My system is a conventional PC with Windows Vista Home Premium, dual core
CPU and 2GB RAM.

I installed a physically diminutive Gizmo Jr USB2 4BG flash drive, setting
aside its entire capacity for ReadyBoost.

Now when I insert it, it shows up as drive F with the following results:

I try to open it by left-clicking:
"Please insert disk into removable disk F"

I try to format it via context menu:
"There is no disk in drive F:. Insert a disk and try again"

I view Properties via context menu:
"Type: Removable Disk
File System: Unknown
Capacity: 0 bytes"

and (elsewhere)
"Windows cannot access the disk"

Also the ReadyBoost tag no longer appears so I cannot reallocate the Gizmo's
space for normal storage of data.

I can see it as a drive and as a named USB device in Device Manager but
cannot get it to respond in any way, and the ReadyBoost tab no longer
appears. It is as though the ReadyBoost service has got turned off (though I
see from System Information that it is set to Auto and is shown as running).

Is there any way I can restore the ReadyBoost service? Or perhaps forcibly
re-format this USB drive so that I can at least use it as a normal removable
device?