I was given an old makerbot dual and have been able to print using it with the new desktop software. However, some files once sliced to the sd card do not extrude filament. I think the firmware needs updating but when I try to update connect to the PC I get a conveyor error. It is running 5.5 and needs update to 7 if possible. Is there any other reason it would not extrude on certain models. Missing Gcode or something?