Wordpress错误 - 第一个参数应该是一个有效的回调

Question

The full error is call_user_func(myannouncer_addcheckbx) [function.call-user-func]: First argument is expected to be a valid callback in /xxxx/xxxxx/xxxxxx/blog/wp-admin/includes/template.php on line 927

Here is my code

add_action( 'add_meta_boxes', 'myannouncercheckboxes' );
function myannouncercheckboxes() {

    add_meta_box('annoncerid', 'WP Annoncer Post', 'myannouncer_addcheckbx', 'post');

}

// display the metabox

function myannouncer_addcheckbx($post) {
    echo 'Set This Post To Be Accessed By Wp Annoncer Customers <input type="checkbox" name="yesaddposttoannoncer" value="yes" /> <br />';
}

Please tell me why This is happening ...I even tried to remove $post in function myannouncer_addcheckbx($post) still get the error.

What am I missing?