Twitter连接失败 - 收到500内部错误

Question

我在网站上使用php框架CodeIgniter进行Twitter连接。问题是，在连接到Twitter并重定向到回调URL后，我总是看到这500错误。

这是我的代码：

public function callback()
{
    if ( $this->input->get('oauth_token') && ($this->session->userdata('twitter_request_token') !== $this->input->get('oauth_token')) ) {
        $this->reset_session();
        echo 'reset session';
        //redirect(base_url('/twitter/auth'));
    } else {
        $access_token = $this->connection->getAccessToken($this->input->get('oauth_verifier'));
        /*echo '<pre>';
        print_r($this->connection);
        echo '</pre>';*/

        if ( $this->connection->http_code == 200 ) {
            $this->session->set_userdata('twitter_access_token', $access_token['oauth_token']);
            $this->session->set_userdata('twitter_access_token_secret', $access_token['oauth_token_secret']);
            $this->session->set_userdata('twitter_user_id', $access_token['user_id']);
            $this->session->set_userdata('twitter_screen_name', $access_token['screen_name']);

            $this->session->unset_userdata('twitter_request_token');
            $this->session->unset_userdata('twitter_request_token_secret');

            echo 'http code 200 - all is fine, user connected';
            //redirect(base_url('/'));
        } else {
            echo 'http code not 200 - not all is fine, user not connected';
            // An error occured. Add your notification code here.
            //redirect(base_url('/'));
        }
    }
}

此时我甚至都不知道为什么这个错误会产生给我...如果我重新加载此错误的页面，那么我看到其他错误：