The report viewer declaration looks correct and the same properties used in our Silverlight demo works correctly. So the problem is most likely related to either the report or the service.
You already have a sample at your disposal - the Visual Studio examples we install along with the product. You can use the Silverlight application and compare the differences or simply restore your project to previous working state and investigate which change causes the problem. Without further information on this we can only guess what is the culprit.
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