Dr Geep:

Solved the problem!!!.

When rendering a one sided square, and to show a texture on one side, and to be transparent on the other side three things have to be done:

1)  Remove backfacing polygons must be checked in the render settings menu.
2)  Every light in the scene has to have ray traced shadows checked in their properties menu.
3)  Have to have raytracing turned on when rendering.

or

1)  Remove backfacing polygons must be checked in the render settings menu
2)  Every light in the scene has to have depth map shadows checked in their properties menu.
3)  Have to have raytracing turned off when rendering.

If you have raytracing turned on, and have depth mapped shadows checked in the lights properties menu, Poser does not render stuff right. Same for raytracing turned off, and ray traced shadows checked in the lights properties menu. Nothing like taking 2 hours to track down the problem.