I had the same problem. I deleted the entry from the registry and then I did a search on my history (click the history icon on the ie and then click search) for the annoying URL (it was a misspell of a link I usually type a lot). Finally I just right clicked and delete and it stopped showing it on the addressbar when I started typing.
The autocomplete is probably done using the registry, and links infavourites & History… So you should delete it from all in which it appears…

Hope this helps!