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
In the device manager under "Storage controllers" I have a strange entry marked with exclamation. I don't remember having any items marked with exclamation in the device manager before. Right now it says "AKTGJNNI IDE Controller", when I go to Properties to see driver details, it says "No driver files are required or have been loaded for this device." When I uninstall this controller and hit "Scan for hardware changes" it appears again, although the name may be different, but still meaningless letters.
I had Daemon Tools installed previously and had some error during uninstall, so I thought this could be a result of that error, and something may not have uninstalled correctly. That's just my guess though.
I'd appreciate any help on how to get rid of this invalid entry.