Problem migrating storyboard from phone 8 app to store 8.1 app

Question

Following is code from my phone 8 app:

<phone:PhoneApplicationPage.Resources>
  <Storyboard x:Name="sb"   Completed="OnCompleted">
     <DoubleAnimation Storyboard.TargetName="LineRotator" Storyboard.TargetProperty="Angle" Duration="0:0:16"  AutoReverse="True" From="0" To="-1440" />
     <DoubleAnimation Storyboard.TargetName="DotTranslator" Storyboard.TargetProperty="X" Duration="0:0:16"  AutoReverse="True" From="0" To="125" />
  </Storyboard>

</phone:PhoneApplicationPage.Resources>

<Canvas Grid.Row="0" x:Name= "WitchCanvas">
   <Path Stroke="Red" Fill="Red" StrokeThickness="2">
      <Path.Data>
         <GeometryGroup>
             <GeometryGroup>
                 <EllipseGeometry Center="235,125" RadiusX="7" RadiusY="7" />
                 <GeometryGroup.Transform>
                     <TranslateTransform x:Name="DotTranslator" X="0" Y="0"/>
                 </GeometryGroup.Transform>
             </GeometryGroup>
                <LineGeometry StartPoint="235,125" EndPoint="360,125"  />
                <GeometryGroup.Transform>
                    <RotateTransform x:Name="LineRotator" CenterX="235" CenterY="125"/>
                </GeometryGroup.Transform>
        </GeometryGroup>
     </Path.Data>
  </Path>
   <ToggleButton Grid.Row="0"  x:Name="Toggle" Content="Start" Canvas.Left="206" Canvas.Top="265" Height="50" Click="OnToggle" Style="{StaticResource ToggleButtonStyle}"/>  
</Canvas>

The above code draws a red dot at the left end of a horizontal red line. In the animation the red line rotates and, simultaneously,  the red dot translates along the red line. Usually the red dot draws a Spiral of Archimedes.

When copied to an 8.1 Store UserControl, there is no animation (and no error!). I assume the problem is with the TargetProperty but after considerable experimentation, searching and playing with code-behind, I conclude that the solution is beyond my pay grade.

All comments appreciated.