Hi okapi, I'm not really sure, but possibly those other programs will only read some certain kinds of entities out of a DXF files and not SPLINE type entities.

Maybe Rhino writes out that rectangle as a POLYLINE type entity in the DXF file and that matches up with what those programs are looking for.

I could probably figure out some more details if you could post 2 example DXF files - one with a rectangle in it that did not work going into those other programs, and one with the rectangle DXF file that does work.

- Michael