XAML: The property 'Resources' is set more than once

I'm getting the following error:

The property 'Resources' is set more than once.

Here is my XAML:

<UserControl.Resources>
    <!--Resource dictionaries for framework stuff-->
    <ResourceDictionary>
        <Style x:Key="MultiLineTextBox" TargetType="TextBox">
            <Setter Property="BorderThickness" Value="0"/>
            <Setter Property="TextWrapping" Value="WrapWithOverflow"/>
        </Style>
        <ResourceDictionary.MergedDictionaries>
            <ResourceDictionary Source="/View;component/Common/ResourceDictionary.xaml"/>
        </ResourceDictionary.MergedDictionaries>
    </ResourceDictionary>

    <!--Convertors needed for proper display-->
    <c:CollapsedIfNegative x:Key="CollapseIfNegative"/>
    <c:VisibleIfNegative x:Key="MakeVisibleIfNegative"/>
    <c:ErrorCodeToString x:Key="ConvertErrorCodeToString"/>
</UserControl.Resources>