Tirta I had that very same problem 2 year ago for roughly 2 weeks.It's definitely your browser.Try clearing all the cookies and refresh your page as well.It solved the problem for me.Also if using explorer try accessing the forum on chrome.This is the browser I am using to answer your question because when I use explorer everytime I log into the forum I get logged out the moment I start moving form post to post...I am going to clear them damn cookies from explorer now...