Is there a way for forums to have like an auto log in or remember me tab? One of my members says that he has to constantly sign in for some odd reason. He told me he doesn't clear his cookies/cache/history as well.
MyBB has a "Remember me" option. You have to check it when you login. Although, if he has to login constantly (= at every page load?) there is something wrong with your cookie settings. Other members don't have this problem? Has he tried to clear his cookies and try it again?