Code:
<head>
<style type="text/css">
#ul1
{
	position:		absolute;
	display:		none;
}
#div_bar > ul > li:hover > ul
{
	display:	inline-block;
}
</style>
</head>
<body>

<div style="height: 100px; background: #FFFF00;"></div>

<div id="div_bar">
    <ul>
        <li>
        <a href="#">Menu Item 1</a>
            <ul id="ul1">
			<li><a href="#">sub item 1</a></li> 
			<li><a href="#">sub item 2</a></li> 
			</ul>
        </li>
    </ul>
</div>
</body>
Above is simple code for a CSS popup menu.
The code is working well under FireFox, but not working under IE8.

Further checking IE8, I found that IE8 doesn't know element > element syntax.

How to figure the problem out for IE?

Thanks for comments.

BTW: you can code all code to a blank HTML page for testing.

.