Error:sequence contains no matching element

Hi,

 i want defaultely string to display in Combo box. i have use this code but i am receiving errors


             HourTypes = new EnumToDropdownMapper().Map().OrderBy(x => x.Description).ToList();---> Error
            var hourtype = HourTypes.Single(type => type.Description == HourType.NormalTime.ToString());
            SelectedHourType = hourtype;


Error:sequence contains no matching element 


Please help me i want to bind from  enum values