.. had a look at the iphone forum, and found this is not an uncommon issue for mobile users.
Paul Cantrell offers this advice:
I think I figured it out. Go to the chess app on facebook and there should be a box where you can either merge your accounts or create a username/pw for your facebook transition account. They email you your password.
Terry (LawTel) has discovered an interesting problem.
He exclusively uses facebook to access chess.com, and so the API is throwing login errors when he tries to connect. Specifically, it says he needs to setup a password.
Anyone know how to setup a password when you already have an existing account via facebook?
anybody? erik? bueller? bueller?