New Post: XamlParseException on xctk:MaskedTextBox

This issue suddenly popped up this morning using VS2015. I'm unsure of exactly what has changed to start causing this issue, but I cannot figure it out.

<Style x:Key="MaskedTextBoxStyle" TargetType="xctk:MaskedTextBox">
        <Setter Property="Foreground" Value="{DynamicResource {x:Static SystemColors.ControlTextBrushKey}}"/>
        <Setter Property="Background" Value="{DynamicResource {x:Static SystemColors.WindowBrushKey}}"/>
        <Setter Property="BorderBrush">
            <Setter.Value>
                <LinearGradientBrush EndPoint="0,20" MappingMode="Absolute" StartPoint="0,0">
                    <GradientStop Color="#FFABADB3" Offset="0.05"/>
                    <GradientStop Color="#FFE2E3EA" Offset="0.07"/>
                    <GradientStop Color="#FFE3E9EF" Offset="1"/>
                </LinearGradientBrush>
            </Setter.Value>
        </Setter>
        <Setter Property="BorderThickness" Value="1"/>
        <Setter Property="Padding" Value="1"/>
        <Setter Property="AllowDrop" Value="True"/>
        <Setter Property="FocusVisualStyle" Value="{x:Null}"/>
        <Setter Property="ScrollViewer.PanningMode" Value="VerticalFirst"/>
        <Setter Property="Stylus.IsFlicksEnabled" Value="False"/>
        <Setter Property="Template">
            <Setter.Value>
                <ControlTemplate TargetType="xctk:MaskedTextBox">
                    <Themes:ListBoxChrome x:Name="Bd" BorderBrush="{TemplateBinding BorderBrush}" BorderThickness="{TemplateBinding BorderThickness}" Background="{TemplateBinding Background}" RenderMouseOver="{TemplateBinding IsMouseOver}" RenderFocused="{TemplateBinding IsKeyboardFocusWithin}" SnapsToDevicePixels="True">
                        <ScrollViewer x:Name="PART_ContentHost" SnapsToDevicePixels="{TemplateBinding SnapsToDevicePixels}"/>
                    </Themes:ListBoxChrome>
                    <ControlTemplate.Triggers>
                        <Trigger Property="IsEnabled" Value="False">
                            <Setter Property="Background" TargetName="Bd" Value="{DynamicResource {x:Static SystemColors.ControlBrushKey}}"/>
                            <Setter Property="Foreground" Value="{DynamicResource {x:Static SystemColors.GrayTextBrushKey}}"/>
                        </Trigger>
                    </ControlTemplate.Triggers>
                </ControlTemplate>
            </Setter.Value>
        </Setter>
        <Style.Triggers>

                --><!--<Trigger Property="HasParsingError" Value="True">
                    <Setter Property="Foreground" Value="Red" />
                </Trigger>

                <Trigger Property="IsMaskCompleted" Value="True">
                    <Setter Property="Foreground" Value="Blue" />
                </Trigger>

                <Trigger Property="IsMaskFull" Value="True">
                    <Setter Property="Foreground" Value="Green" />
                </Trigger>--><!--
          
            <MultiTrigger>
                <MultiTrigger.Conditions>
                    <Condition Property="IsInactiveSelectionHighlightEnabled" Value="True"/>
                    <Condition Property="IsSelectionActive" Value="False"/>
                </MultiTrigger.Conditions>
                <Setter Property="SelectionBrush" Value="{DynamicResource {x:Static SystemColors.InactiveSelectionHighlightBrushKey}}"/>
            </MultiTrigger>
        </Style.Triggers>
    </Style>

This is throwing an XamlParseException that says "Failed to create a 'Type' from text 'xctk:MaskedTextBox'. The inner exception says that it is unable to find the type specified.

Any thoughts?