Hi, Willem
Post your DXF file, Do you have the LazyCam Lic. ?
Now I can see what your trying to do, The lines in the middle should not connect to the outline shape.
If thy don't, In Setup, Loading Options, Connection Line Tol., Set it to .001 or .0001 and re-load your dxf.
Maybe as Dave stated use "Chain-Ent Sel" to select the outer entity's you want, Then use Offset, Then delete them.
Thanks, Chip