Validation problem Div inside ul

[slisebry]

I've got a problem, I'm creating some kind of menu with ul and li but if they click on a link, the menu should go open so more links come out but i'm trying this with <div> inside a <ul> but then I get a validation error, is there something that I can change the code and get the same result?

<ul>
                	<li>Knight Online(USA)</li>
                    <div>
                    	<ul>
                        	<li>News</li>
                            <li>Guides</li>
                            <li>Heavenfire Download</li>
                            <li>Heavenfire Purchase</li>
                        </ul>
                    </div>
                    <li>Hero Online(USA)</li>
                    <div>
                    	<ul>
                        	<li>News</li>
                            <li>Guides</li>
                            <li>Heavenfire Download</li>
                            <li>Heavenfire Purchase</li>
                        </ul>
                    </div>
                </ul>