The tag 'CircularGauge' does not exist in XML namespace

Hi folks,

I created a UserControl with a Circular Gauge inside. It shows up fine in Visual Studio C# 2010 but when I try to open the file with explorer or any other application, I get the following error: The tag 'CircularGauge' does not exist in XML namespace 'http://schemas.actiprosoftware.com/winfx/xaml/gauge'. Line '10' Position '10'.

I have tried solutions to similar issues in this forum but nothing helps.

Here is the code:

<UserControl
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:gauge="http://schemas.actiprosoftware.com/winfx/xaml/gauge"			 
    xmlns:shared="http://schemas.actiprosoftware.com/winfx/xaml/shared"
    xmlns:system="clr-namespace:System;assembly=mscorlib"
    x:Name ="UC" DataContext="{Binding}">
    <Viewbox x:Name="VB" Stretch="Fill">
        <!-- CirularGauge -->        
        <gauge:CircularGauge x:Name="gauge" Width="220" Height="220" Radius="110" HorizontalAlignment="Left" RimBrush="#FF363065" FrameType="CircularThickRimEclipse" BackgroundGeometry="M 1,0 L 2,0 L 3,1 L 3,2 L 2,3 L 1,3 L 0,2 L 0,1 Z" RimGeometry="M 1,0 L 2,0 L 3,1 L 3,2 L 2,3 L 1,3 L 0,2 L 0,1 Z" BackgroundRadiusRatio="0.9" Background="#FFE9DDDD" GlassType="None" IsBackgroundEffectEnabled="True">
        <gauge:CircularGauge.LayoutTransform>
                <ScaleTransform ScaleX="{Binding ElementName=scaleSlider, Path=Value}"
									ScaleY="{Binding ElementName=scaleSlider, Path=Value}" />
            </gauge:CircularGauge.LayoutTransform>

            <gauge:CircularGauge.Items>
                <TextBlock x:Name="textBlock" gauge:CircularGauge.Y="-30" Text="Entrópica" FontFamily="Tahoma"
									Foreground="WhiteSmoke" FontSize="15" />
            </gauge:CircularGauge.Items>

            <gauge:CircularGauge.Scales>
                <gauge:CircularScale Radius="74" StartAngle="180" SweepAngle="180"
									Background="{shared:LinearGradientBrush DarkGray, Gray, GradientType=TopToBottom}">
                    <gauge:CircularScale.TickSets>
                        <gauge:CircularTickSet MajorInterval="20" MinorInterval="5">
                            <gauge:CircularTickSet.Ticks>
                                <gauge:CircularTickMarkMinor TickMarkAscent="3" ScalePlacement="Outside" ScaleOffset="1"
													Background="{shared:LinearGradientBrush Black, DarkGray, GradientType=TopToBottom}" />
                                <gauge:CircularTickMarkMajor ScalePlacement="Outside" ScaleOffset="1"
													Background="{shared:LinearGradientBrush Black, DarkGray, GradientType=TopToBottom}" />
                                <gauge:CircularTickLabelMajor FontFamily="Tahoma" Foreground="WhiteSmoke"
													TextOrientation="Normal" ScalePlacement="Inside" FontStyle="Normal" FontWeight="Normal" ForceCursor="False" MinorInterval="5" />
                            </gauge:CircularTickSet.Ticks>
                            <gauge:CircularTickSet.Pointers>
                                <gauge:CircularPointerNeedle
													Background="{shared:LinearGradientBrush #FFEF153F, #FFEB7A8A, GradientType=LeftToRight, AdditionalStopCount=1}"
													NeedleType="PivotSwordSharp"  PointerExtent="78" PointerAscent="10" BorderWidth="0" gauge:CircularScale.SweepAngle="180" />
                            </gauge:CircularTickSet.Pointers>
                        </gauge:CircularTickSet>
                    </gauge:CircularScale.TickSets>
                </gauge:CircularScale>
            <gauge:CircularScale />
        </gauge:CircularGauge.Scales>
    </gauge:CircularGauge>
    </Viewbox>
</UserControl>

Many thanks in advance,

Christof