Re: 3G modems two similar machines - 1 OK the other not -ideas?
Have you tried plugging it into a different USB port? One of your USB ports might be faulty. Or perhaps your USB's electricity capabilities are overloaded; try unplugging some other USB devices.
I try to treat the cause, not the symptom. I avoid the terminal in instructions, unless it's easier or necessary. My instructions will work within the Ubuntu system, instead of breaking or subverting it. Those are the three guarantees to the helpee.