I am trying to use the Magnifier. I have tried using an example project as well as my own and the designer does not recognise MagnifierManager.Magnifier. I have installed the WPFToolkit.Extended dll using NuGet Package Manager and it is there as a reference and in th eobject browser I can see the objects MagnifierManager and Magnifier. What am I doing wrong? The example code is as follows:-

<Window x:Class="ImageMagnifier.MainWindow"

    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:xt="http://schemas.microsoft.com/winfx/2006/xaml/presentation/toolkit/extended"
    Title="Image Magnifier" Height="350" Width="525">
<Grid>
    <Menu IsMainMenu="True">
        <MenuItem Name="mnuFile" Header="_File" MouseEnter="mnuFile_MouseEnter" MouseLeave="mnuFile_MouseLeave">
            <MenuItem Name="mnuOpen" Header="_Open" Click="mnuOpen_Click"/>
            <Separator/>
            <MenuItem Name="mnuExit" Header="_Exit" Click="mnuExit_Click"/>
        </MenuItem>
        <MenuItem Name="mnuZoom" Header="_Zoom" MouseEnter="mnuZoom_MouseEnter" MouseLeave="mnuZoom_MouseLeave">
            <Slider Name="sliderZoom" Orientation="Horizontal" Minimum="0" Maximum="1" SmallChange="0.025" LargeChange="0.1" Width="100" TickPlacement="Both" TickFrequency="0.1" />
        </MenuItem>
    </Menu>
    <Image Height="269" HorizontalAlignment="Left" Margin="12,30,0,0" Name="image1" Stretch="Uniform" VerticalAlignment="Top" Width="479" />
    <xt:MagnifierManager.Magnifier>
        <xt:Magnifier Name="MyMagnifier" Radius="100" ZoomFactor="0" BorderThickness="3"></xt:Magnifier>
    </xt:MagnifierManager.Magnifier>
</Grid>

</Window>

I have also attached a screen image for the project and the errors