I was using Blend 4 to do some simple animations then copy and pasting the storyboard for use on other objects in my application.  When I executed the Begin() method on the storyboard I would get the following:

Cannot resolve TargetProperty (UIElement.RenderTransform).(CompositeTransform.TranslateY) on specified object.

My XAML was pretty basic.  I finally noticed that Blend had populated the RenderTransform property for me on the working objects.  When I cut and pasted and updated the target object I failed to add the render transform.  Doing so fixes the problem:

Working:

<local:Tile ImageUrl="/SL;component/Images/02_100x100.png" Margin="0,200,0,0" Height="100"
 Width="100" VerticalAlignment="Top" x:Name="Tile_2"
 RenderTransformOrigin="0.5,0.5" >
   <local:Tile.RenderTransform>
        <CompositeTransform/>
   </local:Tile.RenderTransform>
</local:Tile>

Not working:

<local:Tile ImageUrl="/SL;component/Images/02_100x100.png" Margin="0,200,0,0" Height="100"
 Width="100" VerticalAlignment="Top" x:Name="Tile_2"
 RenderTransformOrigin="0.5,0.5" >
</local:Tile>

So if you get this message it is basically telling you that you are missing the RenderTransform property on the target object.