'Controls' is an undeclared prefix; XML is not valid

So here's my xaml: ``` <Window x:Class="KinectButton.Window1" xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" xmlns:Controls="clr-namespace:Coding4Fun.Kinect.Wpf.Controls;assembly=Coding4Fun.Kinect.Wpf" Title="Weather" Height="1024" Width="1280" WindowStartupLocation="CenterScreen"> <Grid x:Name="LayoutRoot"> <Grid.ColumnDefinitions> <ColumnDefinition Width="812*" /> <ColumnDefinition Width="446*" /> </Grid.ColumnDefinitions> <Canvas Background="#FF371780" Grid.ColumnSpan="2"> <Controls:HoverButton Margin="0" Padding="0" x:Name="kinectButton" ImageSize="50" ImageSource="/Images/RightHand.png" ActiveImageSource="/Images/RightHand.png" TimeInterval="2000" Panel.ZIndex="1000" Canvas.Left="0" Canvas.Top="0" /> <Button x:Name="button1" Content="Close" Height="141" Canvas.Left="979" Canvas.Top="6" Width="273" Background="#FFFFF600" FontSize="53.333" Click="button1_Click" BorderThickness="4" Foreground="#FF1A1717" /> <Label Canvas.Left="0" Canvas.Top="733" Content="" Height="1024" Name="message" Width="1280" Foreground="White" FontSize="40" HorizontalContentAlignment="Center" VerticalContentAlignment="Center" /> <Image Height="128" Name="videoStream" Stretch="Fill" Width="191" Canvas.Left="539" Canvas.Top="825" /> </Canvas> </Grid> </Window> ``` And it keeps giving the error: ''Controls' is an undeclared prefix. Line 11, position 14.' XML is not valid.