Validation Group for multiple validator

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ASP.NET

Hi,

I have two link button:

<asp:LinkButton Id="linkButton" Runat="server" CommandName="Report" ValidationGroup="group1">

<asp:LinkButton Id="linkButton2" Runat="server" CommandName="Report" ValidationGroup="group2">

with Two textboxes each:

<asp:TextBox Id="txtStart" Runat="server" MaxLength="11" Width="100"></asp:TextBox>

<asp:TextBox Id="txtEnd" Runat="server" MaxLength="11" Width="100"></asp:TextBox>

then each textbox has a 1 RequiredValidator and 2 CustomValidator:

<asp:RequiredFieldValidator Id="reqB" Runat="server" ValidationGroup="group1" ControlToValidate="txtEnd" ErrorMessage="Please enter an End Date">*</asp:RequiredFieldValidator>

<asp:CustomValidator Id="startValB" Runat="server"  ErrorMessage="Please enter a valid End Date (mm/dd/yy)">*</asp:CustomValidator>

<asp:CustomValidator Id="endValB" Runat="server" ErrorMessage="End Date must be greater than or equal to the Start Date">*</asp:CustomValidator><br>

My question is, on how to create a correct ValidationGroup on these items? Any help would be highly appreciated. Thank you.