Correct cause you need to create a cookie for PHOTOPOST. If you do not click remember me I beleive it uses a session to cookie you into the forum and photopost works with cookies not sessions
However you have other issues. Did you change databases or something? Cause I try to login with the credentials you sent me in photopost and it says invalid login meaning it can not find the user.
First thing to do is to make sure you upgraded all your photopost files by reuploading everything except the config files