Thanks for your reply.  Yes I am using the .net validation controls.

Here is my code:

<asp:Button ID="Button1" runat="server" Text="Test Button" CausesValidation="true" />
            <br />
            &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
            <asp:Label ID="PasswordLabel" runat="server" Text="Zip File Password:" ForeColor="Black"
                Font-Bold="true"></asp:Label>&nbsp;&nbsp; <span class="Red">
                    <obout:OboutTextBox ID="ZipPwdTextBox" runat="server"></obout:OboutTextBox></span><asp:RequiredFieldValidator
                        ID="ZipPwdValidator" runat="server" ErrorMessage="New Password is required for Zip download"
                        ControlToValidate="ZipPwdTextBox" ForeColor="Red"
                Display="Dynamic">*</asp:RequiredFieldValidator>