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,

Thats because the terrainTile array expects a "Terrain", but gets an "object". Just cast the Instantiated oject to Terrain like this: (Terrain)Instantiate(terrainMember....

Getting the same issue even with casting the instantiated as terrain.