validation (xhtml5): the element 'div' cannot be nested within the element 'updatepanel'

I'm using VS2013 Ultimate on Windows 8, the problem is:

when I try to use updatepanel Ajax control it doesn't accept any other control within it such as a div or header!! for example:

<asp:UpdatePanel ID="UpdatePanel1" runat="server">
<div>

</div>
</asp:UpdatePanel>

thn I get this error:

validation (xhtml5): the element 'div' cannot be nested within the element 'updatepanel'

can u pleaseeeeeeeeeeeee help me guys?!