I have the following set of code in my App.xaml:
<Application.Resources>
    <ResourceDictionary>
        <ResourceDictionary.MergedDictionaries>
            <ResourceDictionary Source="/Client.Common;component/Theme/Brushes.xaml"/>
            <ResourceDictionary Source="/Client.Common;component/Theme/Fonts.xaml"/>
            <ResourceDictionary Source="/Client.Common;component/Theme/CoreStyles.xaml"/>
            <ResourceDictionary Source="/Client.Common;component/Theme/SdkStyles.xaml"/>
            <ResourceDictionary Source="/Client.Common;component/Theme/MyAppName.xaml"/>
            <ResourceDictionary Source="/Client.Common;component/Controls/NavigationPanel.xaml"/>
         </ResourceDictionary.MergedDictionaries>
    </ResourceDictionary>
</Application.Resources>
The NavigationPanel.xaml contains a style that looks like this:
<Style x:Key="NavigationPanelListBox" TargetType="ListBox">
    <Setter Property="Background" Value="{StaticResource DarkBackground}" />
    <Lots of XAML>
</Style>
The {StaticResource DarkBackground} is defined in the Brushes.xaml file (i.e. the first resource dictionary). It is defined as
<SolidColorBrush x:Key="DarkBackground" Color="#FF707176" />
in the resource dictionary.
At runtime, I get the following error:
Cannot find a Resource with the Name/Key DarkBackground [Line: 16 Position: 44]
The line numbers and position references the NavigationPanel.xaml resource dictionary in the app.xaml.
I can reference the brush from other controls, just not the included resource dictionary.
Why can I not reference or why does it not resolve the reference to a resource that is higher in the heirarchy of the merged resource dictionary?? What am I missing here?