Tannywheeler, what you describe sounds like something that's happened to me in the past (on other websites), usually because I have set my browser (sometimes without really noticing I was doing so) to block cookies from the site involved, so when I enter my password (or whatever), the website doesn't actually receive it. This may or may not be what's causing your problem, but it might be worth checking whether or not your browser is set to accept cookies from the site in question.

Good luck...