validate checkbox listbox

javascript:
function validateRegionlist(source, args) {
            var chkListRegions = document.getElementById('<%= cblRegion.ClientID %>');
            var chkListinputs = chkListRegions.getElementsByTagName("input");
            for (var i = 0; i < chkListinputs.length; i++) {
                if (chkListinputs[i].checked) {
                    args.IsValid = true;
                    return;
                }
            }
            args.IsValid = false;
        }
________________________________________________________________________________

Html
<div id="dProductID" style="width: 210px; height: 70px; overflow: scroll; background-color: White;
                                            color: Black">
                                            <asp:CheckBoxList ID="cblProductID" runat="server">
                                            </asp:CheckBoxList>
                                        </div>
_________________________________________________________________________________
Validator    
<asp:CustomValidator runat="server" ID="cvRegion" ClientValidationFunction="validateRegionlist"
                                            ErrorMessage="Please select Region" ValidationGroup="CreateITSol"></asp:CustomValidator>