Try and just put the image in the Images folder and change it to
xml code:
<Control xsi:type="ButtonControl" Id="BtnPlane">
<Position Top="165" Width="100" Height="20" Left="10"/>
<Attributes><Align>center</Align></Attributes>
<Image><Name>msn_airplane</Name></Image>
<Caption>Plane</Caption>
</Control>
See if that works.