Regarding Silver Light Loading...!!!

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Silverlight4

HI Sir,

Im Using Visual Studio 2010 Professional.

When i try to open new silver light application the following error occured.

System.NullReferenceException<br />
Object reference not set to an instance of an object.<br />
   at Microsoft.Windows.Design.Platform.SilverlightMetadataContext.SilverlightXamlExtensionImplementations.<getxmlnamespacecompatibilitymappings>d__8.MoveNext()<br />
   at MS.Internal.Design.Metadata.ReflectionProjectNode.BuildSubsumption()<br />
   at MS.Internal.Design.Metadata.ReflectionProjectNode.SubsumingNamespace(Identifier identifier)<br />
   at MS.Internal.Design.Markup.XmlElement.BuildScope(PrefixScope parentScope, IParseContext context)<br />
   at MS.Internal.Design.Markup.XmlElement.ConvertToXaml(XamlElement parent, PrefixScope parentScope, IParseContext context, IMarkupSourceProvider provider)<br />
   at MS.Internal.Design.DocumentModel.DocumentTrees.Markup.XamlSourceDocument.FullParse(Boolean convertToXamlWithErrors)<br />
   at MS.Internal.Design.DocumentModel.DocumentTrees.Markup.XamlSourceDocument.get_RootItem()<br />
   at Microsoft.Windows.Design.DocumentModel.Trees.ModifiableDocumentTree.get_ModifiableRootItem()<br />
   at Microsoft.Windows.Design.DocumentModel.MarkupDocumentManagerBase.get_LoadState()<br />
   at MS.Internal.Host.PersistenceSubsystem.Load()<br />
   at MS.Internal.Host.Designer.Load()<br />
   at MS.Internal.Designer.VSDesigner.Load()<br />
   at MS.Internal.Designer.VSIsolatedDesigner.VSIsolatedView.Load()<br />
   at MS.Internal.Designer.VSIsolatedDesigner.VSIsolatedDesignerFactory.Load(IsolatedView view)<br />
   at MS.Internal.Host.Isolation.IsolatedDesigner.BootstrapProxy.LoadDesigner(IsolatedDesignerFactory factory, IsolatedView view)<br />
   at MS.Internal.Host.Isolation.IsolatedDesigner.BootstrapProxy.LoadDesigner(IsolatedDesignerFactory factory, IsolatedView view)<br />
   at MS.Internal.Host.Isolation.IsolatedDesigner.Load()<br />
   at MS.Internal.Designer.DesignerPane.LoadDesignerView()<br />
<br />

The desiner window (mainpage.xaml) is not opend.

Why??

Any Idea regarding this???

Please Help