Getting error: Unable to add cookies, header already sent.

[VikesRule]

Everytime someone tries to start a thread, we get this error:

Unable to add cookies, header already sent.
File: /home/balls/public_html/forums/includes/functions_newpost.php
Line: 1

It still posts the thread, but there are other quirks that keep happening, including alot of double posts and sometimes when copy+pasting stuff, weird symbols appear in the text, that look like ” and “.

What do we need to do to fix them?

[Dismounted]

Try disabling any modifications running.