Recipient unable to open a dxf 2004 export in his old Autocad

Hi,
V5
I used dxf 2004 solids, on a line drawing with some solids., hiding solids before exporting.
recipient couldnt open it he says.

I had also sent dwg to show the solids and an iges, couldnt open those either.

He has an old AutoCad prog.

what can I try ?

Cheers.
Steve

R12 Natural? It’s about as old/basic as you can get with DXF - like 1995 or something…