how to save multiple checklistbox to database in a single record asp .net

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C#

ASP.NET

SQL

CheckBoxList

I have two checkboxlists CandidateName and Payment, and a dropdownlist. User can do multiple selections in checkboxlists and one selection at dropdownlist. I am populating those data of chechboxlists and dropdownlist to Panel nested inside UpdatePanel which has gridview and this panel. When I click on Add Button to open up Panel, all data is populating. When I tried to save selected checkedbox lists through "for loop", it is not working. When I debug at for loop statement, it is not going inside the loop. How can I have loop working so that it will save in database. Please help me advise. Thank
This is my C# code.

protected void btnAddNew_Click(object sender, EventArgs e)
    {
        try
        {
      
            string strcbl1 = string.Empty;
            string strcbl2 = string.Empty;
           
            compCon = new SqlConnection(strConnectionString);
            compCon.Open();
           

            for (int i = 0; i < cblCandidateName1.Items.Count-1; i++)
            {
                if (cblCandidateName1.Items[i].Selected ==true)
                {
                    strcbl1 = strcbl1 + cblCandidateName1.Items[i].Value.ToString() + ",";
                }
            }

            for (int j = 0; j < cblPayment1.Items.Count - 1; j++)
            {
                if (cblPayment1.Items[j].Selected == true)
                {
                    strcbl2 += cblPayment1.Items[j].Value.ToString() + ",";
                }
            }
string strCourseID = ddlCourseName.Item.SelectedItem.Value.ToString();

           
            string InsertSchedule = "INSERT INTO ScheduleEmail(CANDIDATE_ID, PAYMENT_ID, TEMPLATE_ID)VALUES(@strCID, @strPID, @strCourseID)";
            SqlCommand InsertScheduleCommand = new SqlCommand(InsertSchedule, compCon);
            InsertScheduleCommand.Connection = compCon;

          
            InsertScheduleCommand.Parameters.AddWithValue(@"strCID", strcbl1);
            InsertScheduleCommand.Parameters.AddWithValue(@"strPID", strcbl2);
            InsertScheduleCommand.Parameters.AddWithValue(@"strCourseID", strCourseID);

            InsertScheduleCommand.ExecuteNonQuery();
            compCon.Close();
        }
        catch (Exception ex)
        {
            ShowPopUpMsg("Data is failed to save in table. Please contact your system administrator \n" + ex.ToString());
        }
        finally
        { 
        DispalyGridViewScheduleEmail();
        
        compCon.Close();
        }

    }

This is my html code.

<asp:Panel ID="panelAddNewTitle" runat="server" style="cursor:move;font-family:Tahoma;padding:2px;" HorizontalAlign="Center" BackColor="Blue" ForeColor="White" Height="25" >Add New</asp:Panel><ajaxToolkit:ModalPopupExtender ID="mpe1"  runat="server" TargetControlID="btnAddNew1" PopupControlID="panelAddNew" RepositionMode="RepositionOnWindowResizeAndScroll" DropShadow="true" PopupDragHandleControlID="panelAddNewTitle" BackgroundCssClass="modalBackground"  ></ajaxToolkit:ModalPopupExtender>
      <asp:CheckBoxList ID="cblCandidateName1" runat="server" RepeatColumns="3" RepeatDirection="Horizontal" RepeatLayout="table">   
 <asp:CheckBoxList ID="cblPayment1" runat="server" RepeatDirection="Horizontal" RepeatLayout="Table"></asp:CheckBoxList>
<asp:DropDownList ID="ddlCourseName" runat="server"> 


<asp:Button ID="btnAddNew2" runat="server" Width="70" Text="Add" OnClick="btnAddNew_Click"  ValidationGroup="add"/>
                 
                
                <asp:Button ID="btnCancel1" runat="server" Width="70" Text="Cancel" CausesValidation="false" OnClick="Cancel_Click" ValidationGroup="add"/>
            </div>
        </asp:Panel>