Hi Silva,
don’t know if you’ve solved your problem yet.
I found the same issue when migrating from ubuntu 12 to 16.
The problem is ubuntu 16 (i think 14 also) does not associate the usb:pidvid (the exar one) to the cdc_acm driver automatically.
You can try to modify the udev rules (hard and i cannot make it work correctly), or you can do it manually.
As sudo (maybe sudo su) execute the next line. Sudo doesnot behave well with echo
echo “04e2 1410” >/sys/bus/usb/drivers/cdc_acm/new_id
check your “vid pid” in with lsusb. Write down “bus XXX device YYY”
check driver loaded with lsusb -t, found “bus XXX” and the leaf “device YYY”.
Hope it helps