I just spent a few minutes trying to figure out an odd error I was having in trying to add Kevin's WPF Bag-o-Tricks to my MemoryGame project. Apparently if you make use of such a 3rd party control (or anything with a different app domain) in one XAML file and then attempt to put that XAML page into another XAML page (whose project does not contain a reference to said 3rd party library) you will get this lovely error:

Cannot find type 'Microsoft.Samples.KMoore.WPFSamples.Transition.TransitionPresenter'. The assembly used when compiling might be different than that used when loading and the type is missing.

On its own that error means nothing to me, but thanks to the people over in this thread I got it figured out. Adding a Bag-O-Tricks reference to the project containing the Shell.xaml fixed everything right up. Basically the container of the XAML page needs to have references to the 3rd party library as wel. Just something to keep in mind incase you run into this issue in working with CompositeWPF in conjunction with external control libraries.