Using Blend Preview for VS2012, I couldn't compile the Demo solution for WPF RadControls. I was getting weird errors like "usercontrol is not supported in a Windows Presentation Foundation project".
Did a bit of searching and found and you need to replace all ">x86</Platform>" with ">AnyCPU</Platform>" in the *.csproj files (I just used a Find in Files replace in Notepad++). After that, everything worked fine.
Thanks to this blog post
for the answer