Happens to everybody. It's not a big deal. I doubt there has ever been a taker who scored 100% of the PKs if he had taken more than 50 in his career. Remember England?
IMO Helguson should not take pens. The Chelsea game the Goal Keeper got to the ball nearlly. And in the wigan game he very nearlly got to the first one and did save the second. Hes not the best pen taker.