There may be a bug currently which requires you when changing your account related settings to not only enter your password in the 'confirm' box at the bottom of the form but also in the 'change password' boxes in the middle of it.
The work around is currently to do just that when changing any other settings in that form. Use your same old password in all three boxes.
I'm looking into what is causing this issue, but it should not be a problem in a meantime as long as you do the above.