I noticed a couple of times now, When i write a little longer thread and i go to submit it, it shows that i am not loged in. It like i get logged out automatically. It takes me to a page that says Invalid thread specified If you followed a valid link, please notify the web master. Skip if you read this what is going on.
While I obviously cannot Speak for Skip, I can tell you these forums systems HAVE a setting we use to automatically Log a user off after a set amount of time. Perhaps that's what is happening to you? I have mine set to one hour. On my forums, you get logged off after one hour of no activity. (Typing in a long post, or taking a long time to type it, counts as inactivity.)