'ddlcoursename' has a SelectedValue which is invalid because it does not exist in the list of items. Parameter name: value

protected void Page_Load(object sender, EventArgs e)
        {
            if (!HttpContext.Current.User.Identity.IsAuthenticated)
            {
                FormsAuthentication.RedirectToLoginPage();
              
            }

         studtid  = Request .QueryString ["studentid"];
         studtname = Request.QueryString["studname"];
            try
            {
                lblcoursedetref.Visible = false;
                param = Request.QueryString["studentid"];
                studentname = Request.QueryString["studname"];
                lblstudenname.Text = studentname;
                if (!IsPostBack)
                {

                    if (param != null)
                    {
                        objBS.open();
                        SqlCommand cmd = new SqlCommand("SP_T_COURSE_DETAILS_SELECT", objBS.conn);
                        lblstudenid.Text = param;

                        cmd.CommandType = CommandType.StoredProcedure;
                        //cmd.Parameters.Add("P_COURSE_DET_REF", SqlDbType.Int).Value = Convert.ToDecimal(studentid1);
                        cmd.Parameters.Add("@COURSE_DET_REF", SqlDbType.Int).Direction = ParameterDirection.Output;
                        cmd.Parameters.Add("@STUDENT_ROLL_NO", SqlDbType.Int).Direction = ParameterDirection.Output;
                        cmd.Parameters.Add("@STUDENT_ID", SqlDbType.Int).Value = Convert.ToDecimal(param);

                        cmd.Parameters.Add("@COURSE_ID", SqlDbType.Int).Direction = ParameterDirection.Output;
                        cmd.Parameters.Add("@SEMESTER", SqlDbType.VarChar, 20).Direction = ParameterDirection.Output;
                        cmd.Parameters.Add("@SUBJECT_ID", SqlDbType.Int).Direction = ParameterDirection.Output;
                        cmd.Parameters.Add("@START_YEAR", SqlDbType.Int).Direction = ParameterDirection.Output;
                        cmd.Parameters.Add("@END_YEAR", SqlDbType.Int).Direction = ParameterDirection.Output;
                        cmd.Parameters.Add("@COURSE_DETAILS_STATUS", SqlDbType.VarChar, 1).Direction = ParameterDirection.Output;
                        cmd.Parameters.Add("@LAST_UPDATED_DT", SqlDbType.DateTime).Direction = ParameterDirection.Output;
                        cmd.Parameters.Add("@LAST_UPDATED_BY", SqlDbType.VarChar, 10).Direction = ParameterDirection.Output;
                        cmd.ExecuteNonQuery();
                        lblstudenid.Text = (cmd.Parameters["@STUDENT_ID"].Value).ToString();
                        txtsturollno.Text = (cmd.Parameters["@STUDENT_ROLL_NO"].Value).ToString();
                        lblcoursedetref.Text = (cmd.Parameters["@COURSE_DET_REF"].Value).ToString();


                        ddlcoursename.Text = (cmd.Parameters["@COURSE_ID"].Value).ToString();
                        ddlsemester.Text = (cmd.Parameters["@SEMESTER"].Value).ToString();
                        ddlsubjectname.Text = (cmd.Parameters["@SUBJECT_ID"].Value).ToString();
                        txtstartdate.Text = (cmd.Parameters["@START_YEAR"].Value).ToString();
                        txtenddate.Text = (cmd.Parameters["@END_YEAR"].Value).ToString();
                        ddlstatusu.SelectedValue = (cmd.Parameters["@COURSE_DETAILS_STATUS"].Value).ToString();

                        hypstudent.NavigateUrl = "~/studentinf.aspx?studentid=" + param + "&studname=" + studentname;
                        hypattendance.NavigateUrl = "~/sattendance.aspx?studentid=" + param + "&studname=" + studentname;
                        hypfees.NavigateUrl = "~/sfees.aspx?studentid=" + param + "&studname=" + studentname;
                        hypresult.NavigateUrl = "~/sresult.aspx?studentid=" + param + "&studname=" + studentname;
                        hyptransfer.NavigateUrl = "~/stransfer.aspx?studentid=" + param + "&studname=" + studentname;
                    }

                    

                    else
                    {
                        lblstudenid.Text = studtid.ToString();
                        lblstudenname.Text = studtname.ToString();
                    }
                    if (param == null )
                    {
                        hypstudent.Visible = false;
                        hypattendance.Visible = false;
                        hypfees.Visible = false;
                        hypresult.Visible = false;
                        hyptransfer.Visible = false;
                      
                        butscoursesave.Visible = true;
                        butupdate.Visible = false;
                    }

                    if (lblcoursedetref.Text !="")
                    {
                        butupdate.Visible = true;
                        butscoursesave.Visible = false;
                    }
                    else if (lblcoursedetref.Text == "")
                    {
                        butscoursesave.Visible = true;
                        butupdate.Visible = false;
                    }


                }
                //BindCoursedropdown();

            }
            catch (Exception ex)
            {

                //// Response.Write(ex.ToString());
                if (lblcoursedetref.Text != "")
                {
                    butupdate.Visible = true;
                    butscoursesave.Visible = false;
                }
                else if (lblcoursedetref.Text == "")
                {
                    butscoursesave.Visible = true;
                    butupdate.Visible = false;

                }
                hypstudent.NavigateUrl = "~/studentinf.aspx?studentid=" + param + "&studname=" + studentname;
                hypattendance.NavigateUrl = "~/sattendance.aspx?studentid=" + param + "&studname=" + studentname;
                hypfees.NavigateUrl = "~/sfees.aspx?studentid=" + param + "&studname=" + studentname;
                hypresult.NavigateUrl = "~/sresult.aspx?studentid=" + param + "&studname=" + studentname;
                hyptransfer.NavigateUrl = "~/stransfer.aspx?studentid=" + param + "&studname=" + studentname;
            }
        }