Lots of people have trouble connecting recent CEM40s to a pi. The usual solution is to put a usb hub in between, though there seems to be a variety of experiences about which hubs work best. I use a powered usb2 hub.
Having exhausted every other possibility that I can think of, I 'think' something has gone wrong with the usb connection on the mount itself. When I use tail -f /var/log/syslog in a terminal, when I plug it into the pi, into a nonpowered USB hub (which was the way I could get it to talk to the mount when I got it) or a powered USB hub no additional entries are made in the log file as they are when any other usb is plugged in. I've tried four different cables same thing. Windows won't pick it up either.
It's still in warranty so I'll have to return to the store to get them to have a look.