How to Instantiate into a terrain array?

My code creates tiles of terrains on start, I wanna use SetNeighbors to connect each Instantiated terrain to its neighbors. here is my code:

var terrainMember:Transform; var terrainRow:int=20; var terrainCol:int=20; private var terrainTile:Terrain[] = new Terrain[400]; function Start () {

 for (var row=1;row<terrainRow;row++){
 var newRow = 100*(row-1);
     for(var col=1;col<terrainCol;col++){
         var arrayPosition = col-1+(terrainRow*(row-1));
         var newCol=100*(col-1);
         terrainTile[arrayPosition] = Instantiate(terrainMember,Vector3(newRow,0,newCol),Quaternion.identity);

 }
 }
 }

The problem is on start it only creates one terrain and gives me an error: "Cannot cast from source type to destination type."

I need to have this array so that i can easily assign each terrain its neighbors. Otherwise I tried doing the same thing using a transform array and it just works fine. Any clue? thanks,