It seems to be very common that asp.net menu control is not to be properly displayed in IE8.
I have developed a website which contains a master page and placed a menucontrol in master page.
While running the project the menu is displaying in the content page,but the submenus are not
visible and a compatibility button will be displayed in IE.While turning IE8 to compatibility mode it displays the sub menu too.
But it is not a right thing because the user may not be aware of this and
he will say that the menu is not working in his browser.
This can be solved by adding the below code in the head tag of the master page.
<head>
<meta http-equiv="X-UA-Compatible" content="IE=EmulateIE7" >
<title>
</title>
</head>
Now the menu will work fine it will display all the submenus and will navigate to the pages as required.