I've been having the same problem over the last couple of days. On the login page, have you tried clicking on the "Clear YBW cookies" button? That might help (I've just done this so will let you know if nothing improves for me).
Also, when you get a temporary password emailed to you, are you going into your personal settings to change your current password to something else? I figured that since my old password didn't seem to be working any more, I should update it.
Happens daily to me on my work desktop. Clearing cookies and logging in again fixes it - until the next day.
Home laptop. Same OS version (slightly different build). Same browser version. Same YBW account. No problem.
I guess I need to compare cookies on the two machines. Trouble is its not quite irritating enough to make me fix it. Bone idle I'm afraid /forums/images/graemlins/frown.gif