Hi,
I got the same problem while connecting the Multitech mCard to a Raspberry Pi 2 Model B using exactly the same instructions from @nestorayuso. Because I used the mCard earlier on another server (OpenSuse on Intel i7) without problems, I knew the mCard was fine. In my case the failure to start the concentrator depends on which USB power supply I used. Looking for some clues, I learned that the R-Pi 2 Model 2 has some USB current limiters installed that could prevent the concentrator to start up correctly.
I fixed the problem by adding the following line to the /boot/config.txt file: max_usb_current=1
Then reboot and the concentrator worked fine since then.
I am not sure you have the same issue here, but it may be worth trying.
regards,
Pieter