.net transitions with WPF

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What steps will reproduce the problem?
1. Using transition on a WPF window, passing 'Window.Left' to transition.
2. I had a Invalid cast exception in 
getIntermediateValue(object start, object end, double dPercentage)
when casting 'end'
3. I corrected this fault by using Convert.toDouble()
4. But doesn't seem to work

What is the expected output? What do you see instead?
I would like to have a linear transition like in Winform. The WPF window 
doesn't move at all. The code for the transition is exactly the same as your 
main page:
Transition.run(main_window, "Left", 1000, new 
TransitionType_Deceleration(2000));

What version of the product are you using? On what operating system?
Last version 1.2, WIN64


Please provide any additional information below.
I tried with a Winform, it work pretty well.

Original issue reported on code.google.com by manzh...@gmail.com on 2 Jun 2014 at 5:31