wordpress Warning: Cannot modify header information

after using locate_template() to load template with child theme i get error

Warning: Cannot modify header information - headers already sent by (output started at /xxxx/wp-content/themes/bp-default/header.php:3) in /xxxx/wp-includes/pluggable.php on line 868

here a solution:

------------- edit code --------------------
edit the file wp-includes/pluggable.php
in line 863 replace:

if ( $is_IIS ) {
header("Refresh: 0;url=$location");
} else {
if ( php_sapi_name() != 'cgi-fcgi' )
status_header($status); // This causes problems on IIS and some FastCGI setups
header("Location: $location", true, $status);
}

with this:
if( !headers_sent() ).
{
if ( $is_IIS ) {
header("Refresh: 0;url=$location");
} else {
if ( php_sapi_name() != 'cgi-fcgi' )
tatus_header($status); // This causes problems on IIS and some FastCGI setups
header("Location: $location", true, $status);
}
--------------------------------------------

not a best solution but it get rid of that error