I know the original poster has probably long since solved their problem, but I thought I'd answer for anyone coming along after who faces a similar exception and is confused. Especially since both of the original replies above are either wrong or comment spam.
Now, what this exception generally means is that the XML in the App.Config file is ill-formed. That is, you have probably put something in there that shouldn't be there or something like that. For instance, when I got this error recently, it was because I had accidently put a semi-colon at the end of a key.
I'm not saying this is going to be the answer all the time, but if you get this sort of error, the first thing I would do is go back and check my App.Config file to ensure that you haven't thrown in an extra punctuation mark or the like. Good luck!
Last edited by webbsk; Apr 30th, 2007 at 4:20 pm.