This was confusing me hard....
It works in the example project and does not work in my project.
After some thinking I concluded that the only real difference is that my project is using the NuGet package of AvalonDock.
So I went to the AvalongDock.TesetApp project and deleted the reference to AvalonDock and AvalonDock.Themes.VS2010. I then added the NuGet package "AvalonDock" (version "2.0.0911" (Containing the latest changes the last check in comments).
Once I did that, the AvalongDock.TesetApp project started giving me the same errors my project was giving.
Just to be sure I copied the AvalonDock dlls I built with the AvalonDock source code into my project and it all worked fantastically.
Could there have been an issue with the generation of the latest NuGet package?
(By the way, I love that you use NuGet. It makes getting updates so much easier!)