[asp.net] ModalPopupExtender OK Button click event not firing?

I have a Button inside an UpdatePanel. The button is being used as the OK button for a ModalPopupExtender. For some reason, the button click event is not firing. Any ideas? Am I missing something?

<asp:updatepanel id="UpdatePanel1" runat="server">
    <ContentTemplate>
        <cc1:ModalPopupExtender ID="ModalDialog" runat="server" 
            TargetControlID="OpenDialogLinkButton"
            PopupControlID="ModalDialogPanel" OkControlID="ModalOKButton"
            BackgroundCssClass="ModalBackground">
        </cc1:ModalPopupExtender>
        <asp:Panel ID="ModalDialogPanel" CssClass="ModalPopup" runat="server">
            ...
            <asp:Button ID="ModalOKButton" runat="server" Text="OK" 
                        onclick="ModalOKButton_Click" />
        </asp:Panel>
    </ContentTemplate>
</asp:updatepanel>

None of the previous answers worked for me. I called the postback of the button on the OnOkScript event.

<div>
    <cc1:ModalPopupExtender PopupControlID="Panel1" 
         ID="ModalPopupExtender1"
         runat="server" TargetControlID="LinkButton1" OkControlID="Ok" 
         OnOkScript="__doPostBack('Ok','')">
    </cc1:ModalPopupExtender>

    <asp:LinkButton ID="LinkButton1" runat="server">LinkButton</asp:LinkButton> 
</div>        


<asp:Panel ID="Panel1" runat="server">
    <asp:Button ID="Ok" runat="server" Text="Ok" onclick="Ok_Click" />            
</asp:Panel>   

I was just searching for a solution for this :)

it appears that you can't have OkControlID assign to a control if you want to that control fires an event, just removing this property I got everything working again.

my code (working):

<asp:Panel ID="pnlResetPanelsView" CssClass="modalPopup" runat="server" Style="display:none;">
    <h2>
        Warning</h2>
    <p>
        Do you really want to reset the panels to the default view?</p>
    <div style="text-align: center;">
        <asp:Button ID="btnResetPanelsViewOK" Width="60" runat="server" Text="Yes" 
            CssClass="buttonSuperOfficeLayout" OnClick="btnResetPanelsViewOK_Click" />&nbsp;
        <asp:Button ID="btnResetPanelsViewCancel" Width="60" runat="server" Text="No" CssClass="buttonSuperOfficeLayout" />
    </div>
</asp:Panel>
<ajax:ModalPopupExtender ID="mpeResetPanelsView" runat="server" TargetControlID="btnResetView"
    PopupControlID="pnlResetPanelsView" BackgroundCssClass="modalBackground" DropShadow="true"
    CancelControlID="btnResetPanelsViewCancel" />

I often use a blank label as the TargetControlID. ex. <asp:Label ID="lblghost" runat="server" Text="" />

I've seen two things that cause the click event not fire:
1. you have to remove the OKControlID (as others have mentioned)
2. If you are using field validators you should add CausesValidation="false" on the button.

Both scenarios behaved the same way for me.

None of the previous answers worked for me. I called the postback of the button on the OnOkScript event.

<div>
    <cc1:ModalPopupExtender PopupControlID="Panel1" 
         ID="ModalPopupExtender1"
         runat="server" TargetControlID="LinkButton1" OkControlID="Ok" 
         OnOkScript="__doPostBack('Ok','')">
    </cc1:ModalPopupExtender>

    <asp:LinkButton ID="LinkButton1" runat="server">LinkButton</asp:LinkButton> 
</div>        


<asp:Panel ID="Panel1" runat="server">
    <asp:Button ID="Ok" runat="server" Text="Ok" onclick="Ok_Click" />            
</asp:Panel>   

Put into the Button-Control the Attribute "UseSubmitBehavior=false".

I was just searching for a solution for this :)

it appears that you can't have OkControlID assign to a control if you want to that control fires an event, just removing this property I got everything working again.

my code (working):

<asp:Panel ID="pnlResetPanelsView" CssClass="modalPopup" runat="server" Style="display:none;">
    <h2>
        Warning</h2>
    <p>
        Do you really want to reset the panels to the default view?</p>
    <div style="text-align: center;">
        <asp:Button ID="btnResetPanelsViewOK" Width="60" runat="server" Text="Yes" 
            CssClass="buttonSuperOfficeLayout" OnClick="btnResetPanelsViewOK_Click" />&nbsp;
        <asp:Button ID="btnResetPanelsViewCancel" Width="60" runat="server" Text="No" CssClass="buttonSuperOfficeLayout" />
    </div>
</asp:Panel>
<ajax:ModalPopupExtender ID="mpeResetPanelsView" runat="server" TargetControlID="btnResetView"
    PopupControlID="pnlResetPanelsView" BackgroundCssClass="modalBackground" DropShadow="true"
    CancelControlID="btnResetPanelsViewCancel" />

I've found a way to validate a modalpopup without a postback.

In the ModalPopupExtender I set the OnOkScript to a function e.g ValidateBeforePostBack(), then in the function I call Page_ClientValidate for the validation group I want, do a check and if it fails, keep the modalpopup showing. If it passes, I call __doPostBack.

function ValidateBeforePostBack(){ 
     Page_ClientValidate('MyValidationGroupName'); 
     if (Page_IsValid) { __doPostBack('',''); } 
     else { $find('mpeBehaviourID').show(); } 
}

It appears that a button that is used as the OK or CANCEL button for a ModalPopupExtender cannot have a click event. I tested this out by removing the

OkControlID="ModalOKButton"

from the ModalPopupExtender tag, and the button click fires. I'll need to figure out another way to send the data to the server.

It could also be that the button needs to have CausesValidation="false". That worked for me.