Code works, but warning about call_user_func_array() appears

Somewhere in your theme or plugins, you must have a line like this add_action( 'something', 'yoursite_pre_user_query' ). Find it and remove or fix it.

Also, the get_users function has since been updated. Your first parameter must be an array.

<ul>
<?php
    $blogusers = get_users( array('blog_id' => 1, 'orderby' => 'nicename') );
    foreach ( $blogusers as $user ) {
        echo '<li>Nick: ' . $user->user_nicename . '</li>';
        echo '<li>Name: ' . $user->display_name. '</li>';
        echo '<li>Email: ' . $user->user_email. '</li>';
    }
?>
</ul>