Silverlight DataPager breaks VS designer

I'm experimenting with the Silverlight 4 SDK DataPager. I have some code in my XAML that looks like this:

        <sdk:DataPager 
            x:Name="dataPager1"
            PageSize="100" />

As SOON as I paste that into my XAML the designer breaks with this odd message:

Error HRESULT E_FAIL has been returned from a call to a COM component.

But if I close the designer and re-open then that error goes away. However, the preview in the designer of my user control is completely broken. At runtime it works though开发者_JAVA百科.

Any idea why the DataPager and the designer don't seem to be getting along?

Oddly enough when I tried this again in a new project it did not happen. In the first project where I got this error I manually created the XAML and the references to the DLLs necessary, as well as the XMLNS declarations. In the second project I let Visual Studio take care of it by dragging the control in from the Toolbox. I guess when I did things manually I must've done something to make it not work right in the designer. But I don't know what.