Is there anything else to import than Telerik.Windows.Controls ?
Because if I do :
alert.ShowDuration = 6000
Key.Direction = AnimationDirection.Out,
Key.MinOpacity = 0.5,
Key.MaxOpacity = 0.9,
Key.SpeedRatio = 0.5
the part "manager.ShowAnimation(...)" isn't working (FadeAnimation isn't declared and I have 4 errors like this : "Name of field or property being initialized in an object initializer must start with '.'")