Can you not validate a checkboxlist or something? Here's what I have:
<tr><td><asp:CustomValidator Enabled="true" ID="cusValEntreeSelections" ControlToValidate="chkbxEntreeList" runat="server" onservervalidate="cusValEntreeSelections_ServerValidate" /></td></tr>
<tr><td align="right" ><asp: Go to the complete details ...