PHP Error

It gives me this error “Cannot modify header information – headers already sent in ../…/functions.php on line 3252” with a blank page at loading
the line is
The lines are

3249 function wp_ob_end_flush_all() {
3250	$levels = ob_get_level();
3251    for ($i=0; $i<$levels; $i++)
3252	ob_end_flush();
3253 }