mmm ok. For some reason I couldn't get blend to find the components in the assembly :( When I add the assembly as reference it won't add the components to the component list. Not entirely sure what I did as I'm at work now and don't have access to the machine
which has blend on it. Did you do something special in order to get the components to show up in the component list.
I did try adding the components manually by editing the XAML but that led to the error I was talking about above.
Anyway thanks heaps for your help :)