How can I create Magnifier Component in WPF By using Magnification API

Question

I want to create a WPF component that host a Magnifier so i started with http://msdn.microsoft.com/en-us/library/ms742522.aspx

here's some code http://pastebin.com/tRFYJ1be

And now i have error message: Failed BuildWindowCore when returning the child window handle hosted.

How can i resolve this problem. if there's better solution i'm Here :)

Thank You