codice:
<%@ Page Language="C#" AutoEventWireup="true" CodeFile="button.aspx.cs" Inherits="SqlServer_button" %>

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head id="Head1" runat="server">
    <title></title>
</head>
<body onload="InitValidators()">
    <form id="form1" runat="server">
    <div>
        <asp:TextBox ID="TextBox1" runat="server"></asp:TextBox>
        <asp:TextBox ID="TextBox2" runat="server"></asp:TextBox>
        <%-- <asp:CompareValidator ID="CompareValidator1" runat="server" ErrorMessage="Data non valida"
            ControlToValidate="TextBox2" ControlToCompare="TextBox1" Type="Date" Operator="GreaterThanEqual"
            CssClass="redb" Display="None" SetFocusOnError="false"></asp:CompareValidator> --%>
        <asp:ImageButton ID="Button1" ImageUrl="/webapplication1/Images/confirm.png" runat="server" OnClick="Button1_Click"
            OnClientClick="if(!confirm('Confermi?')) return false;" />
        <asp:RequiredFieldValidator ID="TextBox2_1" runat="server" ControlToValidate="TextBox1"
            ErrorMessage="Inserire periodo temporale di interesse 1" Display="None" Enabled="false"></asp:RequiredFieldValidator>
        

        

        <asp:TextBox ID="TextBox3" runat="server"></asp:TextBox>
        <asp:TextBox ID="TextBox4" runat="server"></asp:TextBox>
        <%-- <asp:CompareValidator ID="CompareValidator2" runat="server" ErrorMessage="Data non valida"
            ControlToValidate="TextBox4" ControlToCompare="TextBox3" Type="Date" Operator="GreaterThanEqual"
            CssClass="redb" Display="None" SetFocusOnError="false"></asp:CompareValidator> --%>
        <asp:ImageButton ID="Button2" ImageUrl="/webapplication1/Images/confirm.png" runat="server" OnClick="Button2_Click"
            OnClientClick="if(!confirm('Confermi?')) return false;" />
        <asp:RequiredFieldValidator ID="TextBox4_1" runat="server" ControlToValidate="TextBox4"
            ErrorMessage="Inserire periodo temporale di interesse 2" Display="None" Enabled="false"></asp:RequiredFieldValidator>
        <asp:Label ID="MessagesLabel" runat="server" Text=""></asp:Label>
        

        

        <asp:ValidationSummary ID="ValidationSummary1" ShowMessageBox="true" runat="server"
            ShowSummary="false" />
    </div>
    </form>
    <script type="text/javascript" language="javascript">
        function InitValidators() {

            var DataInizio = document.getElementById('<%=TextBox1.ClientID%>');
            var DataFine = document.getElementById('<%=TextBox2.ClientID%>')
            var DataInizio1 = document.getElementById('<%=TextBox3.ClientID%>');
            var DataFine1 = document.getElementById('<%=TextBox4.ClientID%>')

            if (DataInizio.value == '' || DataFine.value == '') {                 
                ValidatorEnable(document.getElementById('<%=TextBox2_1.ClientID%>'), true);
                ValidatorEnable(document.getElementById('<%=TextBox4_1.ClientID%>'), false);
            }
        }
    </script>
</body>
</html>