Display nested GridView on Button click of main GridView using C# in ASP.Net

Dear All, I have a Main GridView with a Nested GridView data. I want to retrieve the Nested GridView data based on main GridView ID and Button Click. if the Main GridView ID has a Session value "Yes" then display the Nested GridView with its data on Button Click.

HTML CODE:

<asp:TextBox ID="MyConferenceID" runat="server" Width="50px"> </asp:TextBox>

<asp:Button ID="KonferanseButton" runat="server" Text="Event ID - Get Data" onclick="Konferanse_Click" CausesValidation="false" />

<asp:RadioButtonList ID="chkHasCourseGroup" runat="server" AutoPostBack="true" OnSelectedIndexChanged="chkHasCourseGroup_SelectedIndexChanged" SelectedValue='<%# Eval("HasCourseGroup") %>'>
    <asp:ListItem Text="Yes" Value="Yes"></asp:ListItem>
    <asp:ListItem Text="No" Value="No"></asp:ListItem>
</asp:RadioButtonList>

CODE BEHIND:

protected void Konferanse_Click(object sender, EventArgs e)
{
	string constr = ConfigurationManager.ConnectionStrings["DataConnString"].ConnectionString;
    SqlConnection con = new SqlConnection(constr);
 	con.Open();
 	
    sqlString = "SELECT * from konferanse_Register where CourseID ='" + MyConferenceID.Text.Trim() + "'";
    
    SqlCommand cmd = new SqlCommand(sqlString, con);
    
	if (MyConferenceID.Text != "")
    {
        SqlDataReader reader = cmd.ExecuteReader();
        
        if (reader.Read())
        {
        	chkHasCourseGroup.SelectedValue = reader["HasCourseGroup"].ToString();
        	
        	if (reader["HasCourseGroup"].ToString() == "Yes")
            {
               Gridview3.Visible = true;

               int rowIndex = 0;

               if (ViewState["CurrentTable"] != null)
               {
                  DataTable dt = (DataTable)ViewState["CurrentTable"];

                  if (dt.Rows.Count > 0)
                  {
                     for (int i = 0; i < dt.Rows.Count; i++)
                     {
                         DropDownList ddGroupType    = (DropDownList)Gridview3.Rows[rowIndex].Cells[1].FindControl("dropDownGroupType");
                         TextBox tGroupName          = (TextBox)Gridview3.Rows[rowIndex].Cells[2].FindControl("txtGroupName");

                         Gridview3.Rows[i].Cells[0].Text = Convert.ToString(i + 1);

                         ddGroupType.SelectedValue       = dt.Rows[i]["GroupType"].ToString();
                         tGroupName.Text                 = dt.Rows[i]["GroupName"].ToString();

                         rowIndex++;
                     }
                  }
                  Gridview3.DataSource = dt;
                  Gridview3.DataBind();
               }                                
            }
        }
    }
}

On Event button click, the Nested GridView is not displaying. How to solve this problem?

Many thanks in advance