Ajax long polling with Codeigniter and mysql

Question

I am attempting to implement a simple chat application using ajax long polling with codeigniter framework. Below is the ajax request

var timestamp = null;
function check_incoming_chat_message(me, timestamp) {
$.ajax({
    type: "Get",
    dataType: 'json',
    url: 'http://localhost/ci/index.php/chat/check_chatbox?to_me='+me+'&timestamp='+timestamp, 
    async: true,
    //data: {to_me: me, timestamp: timestamp},
    cache: false,
    success: function(response) {
        setTimeout(check_incoming_chat_message(response.to_chat, response.timestamp),10000);
    },
    error: function(response) {
        setInterval(check_incoming_chat_message(response.to_chat, response.timestamp),2000);
    },
    complete: function() {
    }
});

}

And below is the code at the controller end, in which the control keeps looping checking the db, unless there is a new chat message in the mysql in which case it throws the chat message to the view. And once i get the chat message at the view, i trigger the ajax request again.(atleast thats my idea)

function check_chatbox() {
        $logged_in_user = $_GET["to_me"];
        $last = $_GET["timestamp"];
        header('Content-type: text/plain'); 
        header('Content-type: application/json'); 
        if($last == "" || $last == null) { // check if timestamp is null
            $result = $this->chat_model->current_tstamp($logged_in_user);
            foreach($result as $row)
            {
                $data = array('msg_time' => $row->msg_time,
                              'chat_message' => '',
                              'to_chat' => $logged_in_user
                );
            }
            echo json_encode($data);
            return;
        }
        $result = $this->chat_model->current_tstamp($logged_in_user);
        foreach($result as $row)
        {
            $data_array = array('msg_time' => $row->msg_time);
        }
        $current = $data_array['msg_time'];


        while($current <= $last) {
            usleep(100000);
            //clearstatcache();
            $result = $this->chat_model->current_tstamp($logged_in_user);
            foreach($result as $row)
            {
                $data = array('msg_time' => $row->msg_time);
            }
            $current = $data['msg_time'];
        }
        $result = $this->chat_model->check_new_messages($logged_in_user, $current);
        if($result) {
            foreach($result as $row)
            {
                $data = array('chat_message' => $row->chat_message,
                         'from_chat' => $row->from_chat,
                         'chat_id'   => $row->chat_id,
                         'msg_time'  => $row->msg_time
                );
            }

            echo json_encode($data);
            return;
        }
        else {
            return;
        }
    }

The problem is that, it blocks all the other requests in the page, including hyperlinks(as in anchor tags in codeigniter).Can someone please help me point out as to what i am doing wrong?

Thanks

Note: I am trying to replicate the same procedure used in this example http://www.mediafire.com/download/3xd0zx5ej3pp42b/comet.zip