I think that part that Erin accused a cast member of sexually harrassing her was just a rumor. I know I read about it in the tabloids around the time of the 1992 Happy Days Reunion. The real reason she didn't appear was that she was going through a bad time in her life, mainly the fact that she was going through a divorce. Erin's been happily married to her second husband for 16 years.
The part about Henry not knowing how to ride a motorcycle, Henry has stated this in many of his interviews that he had bad co-ordination. They would push him on the set sitting on the motorcycle to make it look like he was riding it. One thing about Henry though, success never went to his head like Scott Baio.
Complete Series Box Sets I own: MASH, Three's Company, Gilligan's Island, The Dukes Of Hazzard, The Golden Girls, The Monkees, The Brady Bunch, Full House, I Dream Of Jeannie, Bewitched, Taxi, Gimme A Break, Dallas, Charlie's Angels, Joanie Loves Chachi, Laverne & Shirley, Mork & Mindy, The Cosby Show, The Facts of Life, Family Ties.