If you ever receive an "Unable to find the specified file" error in Expression Blend while trying to call a Linked Resource File ( like in a shared assembly where you want to save your shared resources ), called in your app.xaml like this one:
<Application.Resources>
<ResourceDictionary>
<ResourceDictionary.MergedDictionaries>
<ResourceDictionary Source="/YourAssembly;Component/Resources/YourResources.xaml"/>
</ResourceDictionary.MergedDictionaries>
</ResourceDictionary>
</Application.Resources>
Be sure that "YourAssembly" is from a project of type "WPF Custom Control Library" and NOT just a "Class Library".
Hope this helps,