Cannot modify header information - headers already sent

UPDATE:

I just found out that this one might be the one causing problem.

PHP Code:

$data['pending_count']   = ($pending->count * $pending->pages);
$data['paid_count']      = ($paid->count * $paid->pages);
$data['cancelled_count'] = ($cancelled->count * $cancelled->pages); 


I cannot use redirect(site_url('login')); below this code. But if I put redirect before $data[] it works just fine.

Is there any way I can solve my error? Thank you!