Ah, I think I know your problem.
It used to happen that when you accessed sad panda before a week was up, even if you had a valid account it would store a cookie or something and you would always get the white page.
I had to completely delete my browser history to get it to work right, as going back a week or a month didn't do the trick. Moment I deleted it, logged into forums.e-hentai.org and then went to sad panda, everything worked just fine.