If you get this page when trying to view the posts, it is asking you to register with the cafe (you've only registered with Naver so far)
where it says 질문 1 ........... and there's an empty box, just type something in (anything)
the section below that is asking you if you want to use your login name or another nickname for the cafe (by default your login name is used so don't worry about it)
and then type in the letters as shown in the image and tick the little box below that to say that you agree with the cafe's rules.
and that's it. you are free to roam around