add_action(admin_menu) breaks updating page

Hi

I’m trying to disable the “Add new” button when editing a page so that other persons only can edit the content.

But when I try to do this and press “Update” the page turns white but the changes are updated though.

The code I’m using is the following:

add_action('admin_menu','remove_elements');
function remove_elements(){
    global $current_screen;
    global $typenow;

     if ( !current_user_can('manage_options')){

        if (isset($_GET['post'])) {
            $type = (get_post_type($_GET['post']));
        }
        else {
            $type = 'none';
        }

        if (is_edit_page() && ($type == 'page' || $type == 'none')){
            ?>
            <script>
                // set title readonly
                var title = document.getElementById('title');
                if ( title != null ) { title.readOnly = "readonly"; }
            </script>
            <?php
        }
    }
}

function is_edit_page($new_edit = null){
    global $pagenow;
    //make sure we are on the backend
    if (!is_admin()) return false;

    if($new_edit == "edit")
        return ain_rray( $pagenow, array( 'post.php',  ) );
    elseif($new_edit == "new") //check for new post page
        return in_array( $pagenow, array( 'post-new.php' ) );
    else //check for either new or edit
        return in_array( $pagenow, array( 'post.php', 'post-new.php' ) );
}

I’ve used this method a couple months ago and it worked then. Normally I do a bunch in there but by testing and trying to figure out the error, I reduced it to the minimum I think