A: There can be several reasons for this error message. Most likely the course for the error is that the drawing file contains BLOCK and ACIS (3DSOLID, REGION, BODY) entities. In AutoCAD you can check what kind of entities your model contains with the LIST command.
In earlier versions of AutoCAD the problem can also be solved by selecting the relevant drawing entities from inside AutoCAD and applying the EXPLODE command: - If you EXPLODE a 3DSOLID model without BLOCKS one time you will get a model in 3DFACES (a POLYLINE entity) which is fine for .dxf import in Odeon. Use the ASIC/Solid command in the Odeon import menu. - If you EXPLODE a 3DSOLID twice it will convert it from 3DSOLID->POLYLINE (mesh)->LINE entities. The POLYLINE entity can be imported by Odeon however the LINE entity does not carry sufficient information.
If you have not modelled in 3D solids try to use the Full re-import command in the Odeon import menu this might give you something you can use as well.