http://www.icyphoenix.com/viewtopic.php?f=35&t=6001&p=40633#p40633
-----------------------------------
spydie
Sun 21 Jun, 2009 16:44

Re: PHP Warnings "Cannot Modify Header Information - Headers Already Sent By"
-----------------------------------
just reload the page and the problem goes away.

I´ve the same prob with mi installation of .27c

There was a way to  clear cache and the problem goes away aswell.
but i can´t remember how.
I think it was new player or the Steffen who told me how.

Edit :
Just found it 

[quote user="New Player" post="34708"]this disable the cache..let me know if this work

open includes/constants.php

find
[code linenumbers=false]// Cache SQL Queries
define('CACHE_SQL', true); // Caching SQL Queries ON
//define('CACHE_SQL', false); // Caching SQL Queries OFF

// Cache Config Tables
define('CACHE_CFG', true); // Caching Config Tables ON
//define('CACHE_CFG', false); // Caching Config Tables OFF

// Cache CH SQL
define('CACHE_CH_SQL', true); // Caching CH SQL ON
//define('CACHE_CH_SQL', false); // Caching CH SQL OFF[/code]

replace with

[code linenumbers=false]// Cache SQL Queries
//define('CACHE_SQL', true); // Caching SQL Queries ON
define('CACHE_SQL', false); // Caching SQL Queries OFF

// Cache Config Tables
//define('CACHE_CFG', true); // Caching Config Tables ON
define('CACHE_CFG', false); // Caching Config Tables OFF

// Cache CH SQL
//define('CACHE_CH_SQL', true); // Caching CH SQL ON
define('CACHE_CH_SQL', false); // Caching CH SQL OFF[/code][/quote]


That worked for me