Session_start() Issue

I’m having the typical “Warning: session_start() [function.session-start]: Cannot send session cache limiter – headers already sent (output started at /etc etc” message, the problem is that i haven’t modified my code or anything than a couple days ago and this problem just appeared from nowhere, the strange thing is that even changing to the default wordpress template the message still appears.

Maybe i have to do a WordPress reinstall, i know wordpress is a bit sensitive to session vars, but while i was developing and the site was online for months it never showed the warning message.