You guys may well have found this solution already but for anyone else who comes looking.
It's a hangover from daemon tools or another virtual drive program you've used.
find the driver in Windows/system32/drivers
(If you find a suspicious driver google it and see what it is)
Mine was sptd.sys (I'd been using daemon tools lite)
On another forum I heard the driver name might start with st3
Delete it (in my case I renamed and moved it to make sure it worked but didn't screw anything else up)
disable and uninstall the problem device in device manager.
It won't come back when you restart. :D