Codeigniter PostgreSQL查询中的非法字符串偏移服务器问题

我们正在使用PostGreSql数据库，当我们运行下面的代码单元时，它显示错误。

 Severity: Warning
 Message: Illegal string offset 'server'
 Filename: postgre/postgre_driver.php

Message: Cannot modify header information - headers already sent by (output started at       system/core/Exceptions.php:185)

模型代码:

public function tracks_add( $id ) {
    $cnt = 0;
    $date = date('Y-m-d H:i:s');
    $s_title = $this->input->post('s_title');
    $s_singer = $this->input->post('s_singer');
    $s_url = $this->input->post('s_url');
    foreach ($s_title as $s_title) {
        $this->db->set( array('a_id'=> $id, 's_title' => $s_title, 's_singer' => $s_singer[$cnt], 's_url' => $s_url[$cnt], 'date'=> $date) );
        $this->db->insert('soundtracks');
        $cnt++;
    }
}