To be able to use 3D acceleration in your application (and all XNA namespaces), you must enable HardwareAcceleration during plugin initialization. Fortunately, this is easy:
<object data="data:application/x-silverlight-2," type="application/x-silverlight-2" width="100%" height="100%"> [...] <param name="enableGPUAcceleration" value="true" /> [...] </object>
To enable GPU acceleration for applications outside the browser, set the GPU enable option on the project properties page.
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