C#

public static void SortByLastName(ref string[] arrayOfLastNames, ref string[] arrayOfFirstNames, ref string[] arrayOfPlateNum, ref string[] arrayOfType, ref string[] arrayOfYear)
       {
           Console.Clear();

           int vehicleCountInt = 0;

           Console.WriteLine("SHOW DATABASE: SORTING BY LAST NAME\n");

           using (StreamReader countVehicle = new StreamReader("vehiclecount.txt"))
           {
               vehicleCountInt = Int32.Parse(countVehicle.ReadLine());

               countVehicle.Close();
           }

           SortedList<string, string> sortedLastName = new SortedList<string, string>(vehicleCountInt);

           using (StreamReader outputLastNames = new StreamReader("lastnames.txt"))
           {

               for (int i = 0; i < vehicleCountInt; i++)
               {
                   arrayOfLastNames[i] = outputLastNames.ReadLine();

                   string keyVal = arrayOfLastNames[i];

                   sortedLastName.Add(keyVal, arrayOfLastNames[i]); //I'm having a run-time error here that throws the ArgumentException

                   if (!sortedLastName.ContainsKey(keyVal))
                   {
                       sortedLastName.Add(keyVal, arrayOfLastNames[i]);
                   }
                   else
                   {
                       sortedLastName.Remove(keyVal);
                       sortedLastName.Add(keyVal, arrayOfLastNames[i]);
                   }

                   Console.WriteLine("{0}", sortedLastName.Keys[i]);//And sometimes throws the exception ArgumentOutOfRange Exception
               }


               outputLastNames.Close();
           }

       }