serialization problem with datatable (EF)

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ASP.NET

Hi everyone

I got the following runtime error:
Type 'Employee_Schedule.EmployeesDBEntities' in Assembly 'Employee Schedule, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null' is not marked as serializable.

while i'm binding listview to a datatable using this code

public DataTable GetDataSource()
        {
            DataTable dt = new DataTable();
            dt = new DataTable();
            dt.Columns.Add("Id");
            dt.Columns.Add("Day");
            dt.Columns.Add("WorkingDay");
            dt.Columns.Add("Vacation");
            dt.Columns.Add("Holyday");

            var employeeStatus = ctx.EmployeeStatus.Where(a => a.Month == selectedMonth);

            int daysCount = DateTime.DaysInMonth(DateTime.Now.Year, selectedMonth);

            for (int i = 1; i <= daysCount; i++)
            {
                DataRow dr = dt.NewRow();
              dr["Day"] = i.ToString();
                foreach (var item in employeeStatus)
                {
                    if (item.Day == i)
                    {
                        dr["Id"] = item.Id;
                        if (item.DayType == 0)
                        {
                            dr["WorkingDay"] = "1";
                            dr["Vacation"] = "0";
                            dr["Holyday"] = "0";
                        }
                        else if (item.DayType == 1)
                        {
                            dr["WorkingDay"] = "0";
                            dr["Vacation"] = "1";
                            dr["Holyday"] = "0";
                        }
                        else
                        {
                            dr["WorkingDay"] = "0";
                            dr["Vacation"] = "0";
                            dr["Holyday"] = "1";
                        }

                        break;
                    }

                }
                if (string.IsNullOrEmpty(dr["WorkingDay"].ToString()) &&
                            string.IsNullOrEmpty(dr["Vacation"].ToString()) &&
                            string.IsNullOrEmpty(dr["Holyday"].ToString()))
                {
                    dr["Id"] = "0";
                    dr["WorkingDay"] = "0";
                    dr["Vacation"] = "0";
                    dr["Holyday"] = "0";
                }

                dt.Rows.Add(dr);
            }

            return dt;
        }

Any suggestions ??