I guess you have visited this link.. http://folding.stanford.edu/English/FAQ-passkey
If using FireFox, go into Tools/Options/Security, and expand the window with all your passwords. You would also want to 'show all' passwords.
Any that relate to the F@H Console passkey should be deleted, and that would solve the issue, allowing a new passkey to be entered and remembered.
F@H.. to solve mankind's maladies.. in our lifetimes!