Hello,
Well, the first thing I was going to suggest was to try a complete re-install, but you already have done. I seem to remember reading this error in one of the forums, i can't remember the solution or which forum it was, I've got a feeling it was the asp.net forum.
I would check the getting started section of:
http://forums.asp.net/90/ShowForum.aspxand the install section of: http://www.dotnetnuke.com/Community/ForumsDotNetNuke/tabid/795/Default.aspx
I've done some initial searching for you but can't find the thread. - Perhaps if you post in those forums someone will be able to help who has come across the problem.
Let me know what happens so I can pass on the info to anyone else with the problem, thanks,