error code - please help! - Joomla! Forum - community, help and support

i mysteriously starting getting error code on home page. preventing me logging admin control panel.

at bottom i've pasted think approximate place error occuring in script. ideas appreciated!

warning: cannot modify header information - headers sent (output started @ /home/oporto/public_html/includes/joomla.php:12137) in /home/oporto/public_html/includes/joomla.php on line 1443

warning: cannot modify header information - headers sent (output started @ /home/oporto/public_html/includes/joomla.php:12137) in /home/oporto/public_html/includes/joomla.php on line 2871

warning: cannot modify header information - headers sent (output started @ /home/oporto/public_html/includes/joomla.php:12137) in /home/oporto/public_html/index.php on line 226

warning: cannot modify header information - headers sent (output started @ /home/oporto/public_html/includes/joomla.php:12137) in /home/oporto/public_html/index.php on line 227

warning: cannot modify header information - headers sent (output started @ /home/oporto/public_html/includes/joomla.php:12137) in /home/oporto/public_html/index.php on line 228

warning: cannot modify header information - headers sent (output started @ /home/oporto/public_html/includes/joomla.php:12137) in /home/oporto/public_html/index.php on line 229

warning: cannot modify header information - headers sent (output started @ /home/oporto/public_html/includes/joomla.php:12137) in /home/oporto/public_html/index.php on line 230


happening somewhere "here"... ?

[snipped code joomla.php]

/**
* task routing class
* @package joomla
* @abstract
*/
class mosabstracttasker {
/** @var array array of class methods call task */
var $_taskmap
/** @var string name of current task*/
var $_task
/** @var array array of class methods*/
var $_methods
/** @var string url redirect */
var $_redirect
/** @var string message operation of task */
var $_message

// action based access control

/** @var string aco section */
var $_acosection
/** @var string aco section value */
var $_acosectionvalue

/**
* constructor
* @param string set default task
*/
function mosabstracttasker( $default='' ) {

}

/**
* sets access control levels
* @param string aco section (eg, component)
* @param string aco section value (if using constant value)
*/
function setaccesscontrol( $section, $value=null ) {


}
/**
* access control check
*/
function accesscheck( $task ) {


}

/**
* set url redirect browser to
* @param string url
*/
function setredirect( $url, $msg = null ) {

}
/**
* redirects browser
*/
function redirect() {


}
/**
* register (map) task method in class
* @param string task
* @param string name of method in derived class perform task
*/
function registertask( $task, $method ) {


}
/**
* register default task perfrom if mapping not found
* @param string name of method in derived class perform if task not found
*/
function registerdefaulttask( $method ) {

}
/**
* perform task triggering method in derived class
* @param string task perform
* @return mixed value returned function
*/
function performtask( $task ) {

etc.

when did error start occur?
did install new extension / template?

did make changes in configuration.php ?
could check if there aren't spaces before