I think it is because you have used polylines and splines to create the parts of the drawing. I havent met a conversion program yet thet will handle them correctly for profiling. If you draw all of your parts as lines, arcs, and circles you cant go wrong.
Try this test program to see if it works for you.
The drawing is made using my layer template which I use for all of my cad drawings. It consists of all the seperate layers I need to make a valid drawing for my post processor. If you want to keep this layer template simply erase the drawing and then save the empty drawing as a layer template. Then when you want to make another drawing simply start from loading the layer template and draw everything using it, then simply rename the file when you are saving it so that you dont overwrite the template file.

Measuring stand clamp test v1.dxf