Sanple for " RadControls for Wpf" Blend Option - Command was not found

[Mathias]

I try to follow http://www.telerik.com/help/wpf/patterns-and-practices-eventtocommand-blend.html 

I created a new project using Silverlight 4 and added a reference to 

C:\Program Files (x86)\Microsoft SDKs\Expression\Blend 3\Interactivity\Libraries\Silverlight\System.Windows.Interactivity.dll


The project doesn't compile with an error "The property 'Command' was not found in type 'InvokeCommandAction"
 The line has

 <i:InvokeCommandAction Command="{Binding TestCommand, Mode=OneWay}"<br>                                           CommandParameter="{Binding ElementName=xRadGridView, Path=SelectedItem}" />

The version for Telerik Gridview is 2012.1.528.1040

Any idea whats wrong here?

[Mathias]

Added this assembly and now it compiles:

c:\Program Files (x86)\Microsoft SDKs\Expression\Blend\Silverlight\v4.0\Libraries\System.Windows.Interactivity.dll