I was having a pretty consistent issue trying to import a step file (PCB model generated by Altium).
The error was coming from TopoMapper.createTopoNames(). Specifically trying to access DiffuseColor (exception thrown saying object has no attibute "DiffuseColor". I ended up working around it by adding
if hasattr(ob.ViewObject,"ShapeColor"):
around the "manage colors of faces" block.
a2p_import_color.patch
I have very little insight into the inner workings of freecad, nevermind the a2plus code base, but the patch is here for your consideration.
cheers and thanks for providing this tool!
/Tim