Yes, you can. According to the unit and according to the web interface I am back at 4.2.0. You can downgrade anytime within 4.x.x. Of course 4.0.0 was a disk partition change, and the boot sector was then separate. So the lowest would be 4.0.1 or 4.0.2. I can't go back to 3.7 where I started.are you sure you can downgrade the Ecos Firmware?