I get the above message on startup out of my taskbar. I assume the mapped network drive this is referring to is a drive that I no longer connect to (I mapped my roommate's shared drive when we were on a network in my last apartment), but of course there is no possibility of connecting to this drive anymore since I moved.
The problem is that I'll go to My Computer and try to disconnect network drives, and Windows will tell me that I have no network drives to disconnect. I was expecting a drive icon with a red X through it, showing that it isn't available. Instead, I seem to have a phantom drive that I can't seem to unmap, yet is being searched for on startup.