New Post: Error - 'System.Windows.StaticResourceExtension' threw an exception.

Just installed toolkit via NuGet and put the default BusyIndicator on working page:

<xctk:BusyIndicator IsBusy="True" BusyContent="Downloading email..." >
            <ContentControl Style="{StaticResource SampleContent}"/>
</xctk:BusyIndicator>

When I run it I get this error "Provide value on 'System.Windows.StaticResourceExtension' threw an exception."

It looks ok in the designer. I've put the schema reference in xaml, also toolkit in references, and using statement.

Am I missing something?