Array Element Issues

So for the game i am making i require an array to hold 50 string elements. What i want to happen is when the player pushes a button the script randomly chooses a number and finds the corrosponding element. I then want the script to then show the selected element in some sort of GUI output such as a label. I get it to work but after a random number of presses i get an error saying it cannot cast from source type to destination type. I was thinking of changing the script to C# and use lists but the sake of continuity i was just seeing if what i could do was possible.

function OnGUI() {
  if (GUI.Button(Rect(Screen.width/2,Screen.height/2,150,50),Toggle)){
    Song = Random.Range(0,playlist.length);
    ChosenSong = playlist[Song];

Never use the JS Array class. Use generic lists instead, and make sure the type of the variable matches the type of the list.

The maximum index of an array is array.Length-1, not array.Length