Display ModelPopup : as per Code behind condition.

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Ajax

<asp:Button ID="Button1" runat="server" Text="SUBMIT"  OnClick ="Button1_Click" />

 <cc1:ModalPopupExtender ID="ModalPopupExtender1" TargetControlID ="Button1" PopupControlID ="tblMessage" runat="server" CancelControlID ="btnClsPwd">
 </cc1:ModalPopupExtender>

//=========================================Code behind============

protected void Button1_Click(object sender, EventArgs e)
    {
        //if (Some condition)
        //{ Show pop up }
        //else { do not show popup
        
    }

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When user click Button1(ie.TargetControlID)It should check the condtion code written in Button1-click event. if it satisfies then the pop-up should display.
Plz share your ideas.