I recall I answered this question recently? Was it somebody else?
This errors shows that you added a code which "echo"s something or displays an information, sends an HTML code to the browser of the user BEFORE headers are sent. For example to set cookies you need to send headers first and if you use a set cookie command AFTER you already sent some piece of information to user's broswer you get this error. More info can be found in PHP manual..
So whatever code you added to the script you need to remove it to correct the error.