ทำไมใช้ jQuery มากกว่า 2 ตัว แล้วทำงานไม่ได้ รบกวนด้วยครับ !!

<script type="text/javascript" src="lib/jquery.js"></script>
<script type="text/javascript" src="<lib/menu.js"></script>
<script type="text/javascript" src="<lib/jquery.roundabout.js"></script>

                 <div class="top">
                    <ul class="round">
                        <li><img src="images/header1.jpg" alt="" /></li>
                        <li><img src="images/header2.jpg" alt="" /></li>
                        <li><img src="images/header3.jpg" alt="" /></li>
                        <li><img src="images/header4.jpg" alt="" /></li>
                        <li><img src="images/header5.jpg" alt="" /></li>
                        <li><img src="images/header6.jpg" alt="" /></li>
                    </ul>

                    <script type="text/javascript">
                        jQuery(document).ready(function() {
                            jQuery('.round').roundabout();
                        });

                    </script>
                </div>

          <div id="menu">
                    <ul class="menu">
                        <li><a href="#" class="parent"><span>Home</span></a></li>
                        <li><a href="#" class="parent"><span>Product</span></a>
                            <div>
                                <ul>
                                    <li><a href="#"><span>Sub Item 1</span></a></li>
                                    <li><a href="#"><span>Sub Item 2</span></a></li>
                                </ul>
                            </div>
                        </li>
                        <li><a href="#"><span>About us</span></a></li>
                        <li><a href="#"><span>Contact us</span></a></li>
                        <li class="last"><a href="#"><span>Login</span></a></li>
                    </ul>
                </div>

        <script type="text/javascript" src="<?php echo base_url(); ?>lib/jquery.js"></script>
        <script type="text/javascript" src="<?php echo base_url(); ?>lib/menu.js"></script>
        <script type="text/javascript" src="<?php echo base_url(); ?>lib/jquery.roundabout.js"></script>

<script type="text/javascript" src="<?php echo base_url(); ?>lib/jquery.js"></script>
<script type="text/javascript" src="<?php echo base_url(); ?>lib/menu.js"></script>
<script type="text/javascript" src="<?php echo base_url(); ?>lib/jquery.roundabout.js"></script>