Jim,
Select the wall, check OI Palette Render tab to see which part of the wall it has been applied to (Right, Center, Left). If it is there, scroll down & check:
1. Map type = Plane
2. Scale - you may need to increase it for the prop to show.
3. Mapping or Attribute Mapping Tool to adjust position on the wall.
4. If it is tiled, deselect repeat H & V.
It's probably there, just too small or on the wrong side of the wall.
George