The rear gears (6) were not adjusted properly and the biggest cog was allowing the chain to jump off next to the wheel. I know now I should have just adjusted the L-screw. But didn't realize that at the time, so went on the Internet to look.
I wanted to adjust the rear gears, so checked a forum. I was asked to loosen the cable with the chain on the smallest cog and adjust the up and down for the chain and cogs. All good. Then retighten the cable. After that I couldn't get the twister shift to move at all!
So, what did I do wrong?