We've reproduced the problem with the RadGauge control and the internal build you downloaded.
The RadControls_for_Silverlight_2009_2_1009_Trial.zip has incorrect version number for Telerik.Windows.Controls.Gauge.dll.
We will resolve this problem with next internal build. Please, accept our apologies for the inconvenience caused.
Meanwhile, you can take a look at our second beta we released last week.
the Telerik team