When you log in manually, there's a drop down box where you can select how long you want to be logged in for. If you've selected "Forever" and it's not working, then you may need to check your browser security settings - if you have them set too high, it won't allow you to accept COL's cookie (cookies are what enable you to have automatic log-ins to forums). Alternatively, you may have a corrupt cookie so you should try clearing your cookies and starting the log-in process again from scratch.
