DXFOUT to remove line types:
1. Open the file with AutoCAD LT.
2. DXFOUT the full file.
3. In a new file DXFIN the file created in previous step.
4. After importing the DXF, generate a new DXF file (DXFOUT).
5. In a new file DXFIN the file created in previous step.
6. Purge all.
7. Save the file.