VS2008 Designer Support?

I'm evaluating SandRibbon for a project I'm working on.  When I type the following XAML into VS2008 RTM the designer won't load complaining that it could not create an instance of the type Ribbon.

<sr:RibbonWindow x:Class="SandRibbonDemo.Window1"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:sr="clr-namespace:Divelements.SandRibbon;assembly=Divelements.SandRibbon"
    Title="Window1" Height="300" Width="300">
    <sr:RibbonWindow.Ribbon>
        <sr:Ribbon>
            <sr:Ribbon.ApplicationPopup>
                <sr:ApplicationPopup>
                    <sr:ApplicationPopup>
                        <sr:MenuItem Text="Test"/>
                    </sr:ApplicationPopup>
                </sr:ApplicationPopup>
            </sr:Ribbon.ApplicationPopup>
        </sr:Ribbon>
    </sr:RibbonWindow.Ribbon>
</sr:RibbonWindow>

However, the application runs fine.  Is this a design time only issue?

Hmm, which version are you using? Full designer support is due in the forthcoming version but the current release should not stop the designer from loading.