Errors in Event Viewer

I've noticed an error (repeated 4 times) in my Event Viewer for Vista
Ultimate.

It is Event ID 24620 from BitLocker-Driver. I don't use BitLocker and
was wondering how it gets turned on? It's checking 4 flash-media ports
plugged into a USB port each time I boot. Example error message:
"Encrypted volume check: Volume information on H: cannot be read."
Nothing was inserted into this port.

I've tried searching Google (web and groups) without finding much at
all.

Thanks.

Sam
--
"We have met the enemy, and he is us" -- Pogo