Assembly not found

Helix 3D Toolkit library I downloaded and tried to use it in my project but I get this error.

"Assembly HelixToolkit.Wpf was not found"

"Assembly HelixToolkit.Wpf.Input was not found"

This is code xaml:

 xmlns:helix="clr-namespace:HelixToolkit.Wpf;assembly=HelixToolkit.Wpf"
 xmlns:helixInput="clr-namespace:HelixToolkit.Wpf.Input;assembly=HelixToolkit.Wpf.Input"

I put a picture to see that I added the anssembly

http://i60.tinypic.com/jp989k.jpg