I want the objects  to cast a shadow still but the back wall is scenery  and I don't want the shadow to appear on it .is there a way to do that out side of casting the light in a differnt way?

By scenery, do you mean it is a background photo, a cyclorama, or an actual background scenery model? What kind of shadows are you using? Depth map or Ray Trace? 

Render the scene in two parts.  One without the back wall and one with the back wall only.  Save the renders as PNG or TIF, then comp in Photoshop. 

 I was talking about  a cyclorama in this case  and raytrace... I ennded up solving it by shortening the cut off on the light. but if there is another way I'd love to know

Quote -  I was talking about  a cyclorama in this case  and raytrace... I ennded up solving it by shortening the cut off on the light. but if there is another way I'd love to know

See my post above.

The only other alternative would be to plug any image map into the ambient channel PoserSurface and set it's value to 1.  The self illumination will eliminate any shadow cast upon it.

You can also plug the texture in Alternate_Diffuse instead of the Diffuse_Color channel and no shadows will be cast.

with GIvariables activated (poser 7 and later), alt_diff and ambient channels may cause surfaces
to appear to emit lite.  izzy and bill may have some way of fixing it so that the alt_diff surface is
not affected by the poser directional lites (poser 8 and later) whilst also preventing the backdrop
from illuminating the scene.  the quick fix is to leave IDL unchecked.

The above solutions are good to prevent something from receiving a shadow. But if a shadow would normally be cast upon your backdrop and suddenly stops at its base, it will be painfully obvious that it IS a backdrop. Better in my opinion to change the light source so the shadow does not fall upon the backdrop.