My problem is similar to this one with that difference I am using SL4 and RadControls_for_Silverlight_2010_1_0309_TRIAL build.
I downloaded the sample application attached in that thread and it worked ( with ddl version 2009.3.1313.1040 ) but when i add dlls version 2010.1.422.1030 it just stop working. Can you help me?