Chill out. There's been so many posts on this subject, it's like
. There's a thread about this at least once a week.
Search "limp mode". You will find page after page of previous posts on this problem.
I've experienced it 8 to 10 times-I lost count. It can be anything from fretting of the pins on the throttle body connector to broken wires on the throttle body wiring harness to bad grip sensor to broken wiring in the harness from the grip sensor to bad connections at the ECM connector. I've had 'em all, except broken wires on throttle body connector harness (hope I haven't jinxed myself
It's very frustrating and aggravating if you are one of the lucky ones to have this problem. My bike has 70000 mi on it and it still goes into limp mode every once in a while, so I don't think it's ever going to end.
Even though I'm really pissed off about it, I don't think it's a very wide spread problem or HD would do something about it-unless they can't fix it or they're not worried about it.
Good luck to your friend.