When I hook it up directly (via USB for now) Simplify3D's Machine Control Panel seems to send the right messages to my BigBox Dual. I can move all the axes including the extruders, but when I slice a file, save it to SD and try to print from the SD, everything happens as it should except extrusion. Preheats OK, then goes through the motions OK, but the extruder gear doesn't even turn. I'm missing something (obviously) but can't figure out what. Help would be greatly appreciated.