If you are getting the similar “UnKnown Namespace ” Error like the one shown in the screenshot below when using the Telerik RadControls for Windows Phone , then it might be because of the wrong namespace being declared in the PhoneApplicationPage.
The type ‘RadRating’ was not found because ‘http://schemas.telerik.com/windowsphone’ is an unknown namespace. [Line: 32 Position: 114]
I got this error when using the RadRating control in a sample WP7 project .
To fix the above error , i modified the name space in XAML page
From
xmlns:telerik=”http://schemas.telerik.com/windowsphone”
To
xmlns:telerik=”clr-namespace:Telerik.Windows.Controls;assembly=Telerik.Windows.Controls.Input”
Thats it . Everything started working normally 
{{ parent.title || parent.header.title}}
{{ parent.tldr }}
{{ parent.linkDescription }}
{{ parent.urlSource.name }}