The only way to make something 'act' as a solid to an actor is to check to make sure that the image of any potential solids do not intersects with its image. After an actor moves, check for intersection with the Wall object and move the actor back off it if intersection occurs. You can make use of the collision detection methods provided in the Actor class. Refer to the documentation if needed.

Explain. Give any error messages. Give details about unwanted behaviors. Supply code (use the 'code' link below the reply box to insert code into posts). Anything that might help resolve the issue. BTW, you can only save the world after compiling or resetting and making changes manually but before any act cycles have been executed.