Ok, I think I have two (maybe unrelated) issues. First let me say that everything was working fine for months until recently. The first issue seems to be a classic "octoprint can't connect to rumba via usb". I know that one of the solution is to follow the troubleshooting here : http://reprap.org/wiki/RUMBA#USB_connection_.28Writing_in_progress.29 to flash the usb firmware. But I always fail to switch to DFU mode : TX and RX leds never flash, and connection is still not possible). This is sad but as I was still able to print directly from the SD card, it was not critical. But since some days ago, this doesn't work. Now, whenever I start a print, the process hangs with a "print from sd : stufftoprint.stl" message on the display. The timer increments but nothing move/heat/anything. At first I was able to solve this by a power off/on then retry. Troublesome, but again, not critical. But it doesn't solve it any more. Each restart is now resulting in this hang situation. So I'm kind of stuck and not sure what to do. Edit (kinda) : During the writing of this post, I tested something stupid/strange I found searching for a solution of the usb issue. And it worked. SD print is back again if I switch to USB power mode but still switch the power on. (jumper is on usb power mode when powering on the bigbox). This feel a bit dirty and I'm not sure it is a good idea to print like that.