I know this question has been answered for a long time, but I would like to add that there is a very good wrapper here. This is the new version of the openCV wrapper that you tried on code project. I've tried it for a couple of days and everything works perfect. Also, I got it working in minutes.
I don't know for the compatibility with mono but under Visual Studio 2010, it works like a charm and saved me ton's of time and money (my project is commercial and most of the library are open source with licence that doesn't allow commercial utilisation unless publishing the code)
