Hmm, try replacing class_session with a fresh copy.
Nope =/ Fresh download of the MyBB packet for just that one file. Still didn't work
Well, what did you do last and did it happen after anything you did?
No plugins; it's a fresh install. Last thing that happened was me entering the Admin account details and my internet connection went fuzzy for about a minute and It said the install was done. So I added the "lock" and went to the index.php and this was there.
If it is fresh, i recomend just redoing it from scratch.
Ok =P I'll get to it in the morning. Thanks guys
Looks like you've somehow deleted your guest usergroup, can you see if it's in phpMyAdmin??