He said his problem came from his 128GB SD card because it was too big. He formatted a 90GB partition and then it worked.BigBlueMenu.3ds always crashes my N3DS and leaves me with one of these "Please power off your device"-messages.
I found this thread:
http://www.logic-sunrise.com/forums/topic/66628-lancer-big-blue-menu-impossible/
but I don't speak French at all.
This is what the message should look like in English.
This kind of error message is sometimes related to SD card, so I would suggest formatting your SD card with SD Formatter (with FORMAT SIZE ADJUSTMENT set to ON).