There are bogus errors hanging around, but at runtime everything works.

Right now, I'm getting Cannot locate resource 'img/icons/silk/arrow_refresh.png'.

I've got a simple UserControl called ImageButton (doesn't everyone?):

<UserControl x:Class="WinDispatchClientWpf.src.controls.ImageButton"
             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
             xmlns:d="http://schemas.microsoft.com/expression/blend/2008" 
             mc:Ignorable="d">
    <Button Name="btnButton" Click="btnButton_Click">
        <StackPanel Orientation="Horizontal">
            <Image Name="btnImage" Stretch="None" />
            <TextBlock Name="btnText" />
        </StackPanel>
    </Button>
</UserControl>

Which does what you'd expect:

[ContentProperty("Text")]
public partial class ImageButton : UserControl
{
    public String Image { set { btnImage.Source = GuiUtil.CreateBitmapImage(value); } }
    public String Text { set { btnText.Text = value; } }
    public double Gap { set { btnImage.Margin = new Thickness(0, 0, value, 0); } }
    public bool ToolBarStyle { set { if (value) { 
        btnButton.Style = (Style)FindResource(ToolBar.ButtonStyleKey); } }
    }
    public bool IsCancel { set { btnButton.IsCancel = value; } }
    public bool IsDefault { set { btnButton.IsDefault = value; } }

    public event RoutedEventHandler Click;

    public ImageButton()
    {
        InitializeComponent();
    }

    private void btnButton_Click(object sender, RoutedEventArgs e)
    {
        if (Click != null)
        {
            Click(sender, e);
        }
    }
}

Where CreateBitmapImage is the following:

public static BitmapImage CreateBitmapImage(string imagePath)
{
    BitmapImage icon = new BitmapImage();
    icon.BeginInit();
    icon.UriSource = new Uri(String.Format("pack://application:,,,/{0}", imagePath));
    icon.EndInit();
    return icon;
}

I can't see the design view of any xaml file that uses an ImageButton like such:

<Window
    foo="bar"
    xmlns:wpfControl="clr-namespace:MyProj.src.controls">
    <Grid>
        <wpfControl:ImageButton ToolBarStyle="True" Gap="3" 
            Click="btnRefresh_Click" Text="Refresh"
            Image="img/icons/silk/arrow_refresh.png" />
    </Grid>
</Window>

Why is VS complaining?