<asp:TextBox ID="_defineTextBox" runat="server"  Width="40px" />
                <asp:CustomValidator ID="_defineTextValidator" runat="server" ControlToValidate="_defineTextBox"
                 OnServerValidate="Define_OnServerValidate"  Display="Dynamic"  ErrorMessage="Must be between 0.00% and 100.00%." ForeColor="Red" 
                 SetFocusOnError="True" ToolTip="0.00%-100.00%" >*</asp:CustomValidator>

protected void Define_OnServerValidate(object source, ServerValidateEventArgs args)
        {
            bool valid = true;
            decimal output = -1.0M;
            if (!string.IsNullOrWhiteSpace(args.Value))
            {
                var amount = args.Value.Replace(CurrencyTye, "");
                var value = decimal.TryParse(amount, out output) ? output : -1.0M;
                if (value < 0M || value > 100.00M)
                    valid = false;
                else
                    valid= true;
            }
            args.IsValid = valid;
        }