IE10 and Modal Popup Extender always visible

Question

It seems that my Modal Popup Extenders are always visible when using IE10.

<ajx:ModalPopupExtender runat="server" ID="mpeNewTest" 
    PopupControlID="pnlTest" TargetControlID="btnNew"
    DropShadow="true" BackgroundCssClass="modalBackground"  />
<asp:Panel runat="server" ID="pnlTest" 
    CssClass="ModalWindow" ScrollBars="Auto">
<!--Stuff here -->
</asp:Panel>

Is there something that is missing? I've looked online and no one seems to have this problem.

The CSS is simple:

.ModalWindow {border: solid 1px #c0c0c0;background:#f0f0f0;
     padding: 10px 10px 10px 10px;width: 800px;height: 500px;}

It seems strange but do I have to add a display:none to the CSS? Or is there another way to get them to be invisible in IE10?

EDIT: I will add that it works in Firefox, Safari and Chrome.

EDIT 2: After some digging I have found I'm getting two errors:

SCRIPT5007: Unable to get property 'PageRequestManager' of 
     undefined or null reference 
SCRIPT5022: Sys.ArgumentException: Value must not be 
     null for Controls and Behaviors.

I've never seen these errors before.

Answer 1

I've managed to find a solution to this problem.

Here you can find the bug fix for ASP.Net.

The header for the article in question is: Bug and Fix: ASP.NET fails to detect IE10 causing _doPostBack is undefined JavaScript error or maintain FF5 scrollbar position

Which is the underlying problem of the error messages I was receiving.