I just tried and it works for me too. Actually, although this was a problem with your cookies, I'm quite sure I caused it. The week before last I introduced, and then immediately detected, a bug in the way that the forum handles the login cookie. You must have created one of these bad cookies in the brief time that the bug was present.
And for those who are reading this and thinking "Huh? Cookies??", I should explain that a cookie is a little piece of data that the browser can store. When a site like YLF can keep you logged in over multiple sessions (i.e. you log in and the next time you come back to the site you are still logged in), it is because the site has asked the browser to "remember" YLF by storing a little login cookie.