Acmellouddine,
Yes, you can not offset a 3D-polyline, because 3D has one axis to much.
You can make a detour: Copy the 3D-P -> "flatten" -> offset into the direction you need -> join the polyline.
BUT you have to use Lisptools to do that.
http://www.4d-technologies.com/geoto...tool_set_1.htm
http://www.glamsen.se/CadTools.htm
Lothar