Need to restart MacBook otherwise my MBox is not recognised

Since the beginning I have a very annoying problem: my MBox works perfectly until I have to disconnect the USB of the MBox from my Macbook. As soon as I connect my MBox without restarting my Macbook, the MBox is not recognised anymore. It is a quite annoying problem since every system restart takes time and interrupts my normal work flow. Does anyone have an idea what the problem could be? I updated already and installed the newest driver but appearently the problem was not solved by this. Thank you for any hints. Cheers.