C# CSS Asp: Menu problem

I have a menu with a submenu. The following is the code for the menu on the site master

<div id="menu">
    <h2>
        Dashboard</h2>
    <asp:Menu ID="NavigationMenu" dir="rtl" runat="server" CssClass="menu"  EnableViewState="false"
       Orientation="Vertical">

        <Items>
            <asp:MenuItem NavigateUrl="~/Vi.aspx" Text="View "/>
                <asp:MenuItem NavigateUrl="~/I.aspx" Text="Import"/>
                <asp:MenuItem NavigateUrl="~/S.aspx" Text="Insert "/>
                <asp:MenuItem NavigateUrl="~/R.aspx" Text="Reports"/>
                <asp:MenuItem NavigateUrl="~/Re.aspx" Text="Re" />
                <asp:MenuItem Text="Maintenance">
                 <asp:MenuItem NavigateUrl="~/F.aspx" Text="For" />
                <asp:MenuItem NavigateUrl="~/P.aspx" Text="Prod" />
                <asp:MenuItem NavigateUrl="~/T.aspx" Text="T" />
                <asp:MenuItem NavigateUrl="~/U.aspx" Text="U" />
                <asp:MenuItem NavigateUrl="~/C.aspx" Text="C" />
          </asp:MenuItem>  &开发者_C百科lt;/Items>
    </asp:Menu>
</div>

The problem is that when i open the submenu it is overlapping the gridview on the page and it not a matter of z-index the background seems to be transparent but i dont want it transparent

There are some issues with Z Index not being handled as planned always when working with master pages.. Where messing around with a similar problem a while back and this forum post helped me: http://forums.asp.net/t/1038006.aspx