Disk Drive ejecting itself

My Time Machine disk drive has been "ejecting" itself since I installed Snow Leopard. I'm not unplugging it, or turning it off. I'm not touching it.
I'm getting the following error message:
"The disk was not ejected properly. If possible, always eject a disk before unplugging it or turning it off."

My question is why would a disk drive be "ejecting" itself. I've turned off the auto backups, and unselected the drive as the backup disk. It is still "ejecting" itself which leads me to believe the problem isn't with Time Machine but with something else - something connected with Snow Leopard because this wasn't happening five days ago before I installed SL.