Error with silverlight application

I've been trying to make a silverlight application (I think this goes here, as I'm using vb.net for it) but I can't even begin to make the application because I get this error:


The XAML is

<UserControl x:Class="SilverlightApplication6.MainPage"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    mc:Ignorable="d"
    d:DesignHeight="300" d:DesignWidth="400">

    <Grid x:Name="LayoutRoot" Background="White">

    </Grid>
</UserControl>

and the details of the error are:

System.NullReferenceException
Object reference not set to an instance of an object.
at Microsoft.Windows.Design.Platform.SilverlightMetadataContext.SilverlightXamlExtensionImplementations.<GetXmlNamespaceCompatibilityMappings>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()
at MS.Internal.Designer.DesignerPane.LoadDesignerView()

I want to fix the error, because I can't load the designer to actually do anything. The only explanation I could think of was that the links in the XAML like 'http://schemas.microsoft.com/winfx/2006/xaml/presentation' are out of date, because when I go to them it says: 'An error occurred while processing your request.'. So any solution to this will be appreciated. Thanks in advance.
~Lukee9