Exception in xaml while opening the Silverlight 4 project

Today i encounter a strange thing. Yesterday all my code was working fine i test it twice before shutting down my pc. Today when i try to open my project exception arrives "System.NullReferenceException Object reference not set to an instance of an object." I searched for the solutions, but none works for me. I did not upgrade silverlight version, i start my work with silverlight 4 and cuurently i am using the same. Here is the stack trace for the exception:


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

Hopefully your suggestions will solve my problem.

Solution

After trying for 3-4 hours i go for simple aproach and it works! Here is what i do:

Go to Add/Remove Program and uninstall all silverlight application, all of them.
Rebbot my pc, install SL4 tools, SL4 Toolkit and SL4 Developer runtime.
Make sure that you change the option for SL4 to update its version automatically.
Another reboot and it's done

I suspect that as i did not change the default setting so SL4 updated itself to SL5 without notifying me :) Make sure to disable automatic updates.