I've always had similar problems when trying to post a reply.
I always get "Welcome back BigKev" then I try to post something and get the 'Log In' screen. After logging in 10 or 12 times it generally recognises me.
I don't like to tick any 'Remember Me' boxes as other people often use my computer when I am out of the office but, if that's what it takes, I'll give it a go.
