XAML Namespace http://schemas.microsoft.com/winfx/2006/xaml is not resolved

I'm using Visual Studio 2010 Express, working on a Silverlight 4 project in C#. This started happening all of a sudden in my project, I get the error that this XAML Namespace is not resolved:

XAML Namespace http://schemas.microsoft.com/winfx/2006/xaml is not resolved

If it helps, here is the section of the XAML file in which the error is being raised:

<ResourceDictionary xmlns:my="clr-namespace:System.Windows.Controls;assembly=System.Windows.Controls.Toolkit"
                xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
                xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
                xmlns:GetGlue="clr-namespace:GetGluePlugin;assembly=GetGluePlugin"
                xmlns:System="clr-namespace:System;assembly=mscorlib"
开发者_如何学Python                xmlns:utils="clr-namespace:Seesmic.Sdp.Utils;assembly=Seesmic.Sdp.Utils">

What could the problem be?

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Is this what you're seeing...

http://laumania.net/2010/06/21/a-possible-solution-to-the-error-xaml-namespace-httpschemas-microsoft-comexpressionblend2008-is-not-resolved/

... or this...

http://social.expression.microsoft.com/Forums/en/blend/thread/e180becd-5e59-4b1d-bd06-9a9547b4e68f

Both relate to Blend removing an attribute and breaking your XAML. It removes (or forgets to add) the mc:Ignorable="d" attribute to UserControls.

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Try adding the WindowsBase and PresentationCore assembly again:

<add assembly="WindowsBase, Version=4.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35" />

<add assembly="PresentationCore, Version=4.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35"/>"

For me this seems to resolve the problem..

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I got this problem when I copied a Resource Dictionary file from another project. I think that it must be a VS 2010 bug or something because it was cured by creating a new ResourceDictionary! I then deleted the new Dictionary that I didn't need.