Reference Error: webform_FireDefaultButton is not defined

Hello,

I currently have a problem with webform_FireDefaultButton not defined.  I've read in previous post that it can be fixed by turning off the ISAPI filters.  My question is if turning off the ISAPI filters is not possible is there another way to fix this?  I currently have a content holder holding the panel.  The panel has being set a default button which resides within.

<asp:Content ID="contentCenterTop" ContentPlaceHolderID="CenterTopPlaceHolder" runat="Server"> <div> <asp:Panel ID="pnl1" runat="server" DefaultButton="cmdCreateUser"> <asp:Table ID="tblSignUp" runat="server"> <asp:TableRow ID="row1" runat="server"> <asp:TableCell ID="cell1" runat="server" ColumnSpan=" ...