2D array error object does not support slicing

Hey everyone, I'm trying to make a grid using a 2d array and I need some help. I keep getting an error at line 39 and 75, The error states that the object does not support slicing. Is there a better way to do this? The lines I'm having problems with look like this:

 aGrid[i][j] = new Card;
 var card:Object = aGrid[i][j];

here is a good chunk of code that shows the variable and the loops i have for this array.

 var aGrid:Array;

 for (var i=0; i<rows; i++){
 aGrid[i] = new Array();
 
  for(var j=0; j<cols; j++){
  aGrid[i][j] = new Card();
  }
 }
 
 


 function BuildGrid()
 {
 GUILayout.BeginVertical();
 for(var i=0; i<rows; i++)
 {
 GUILayout.BeginHorizontal();
 for(var j=0; j<cols; j++)
 {
 var card:Object = aGrid[i][j];
 if(GUILayout.Button(Resources.Load(card),
 GUILayout.Width(cardW)))
 {
 Debug.Log(card);
 }
 }
 GUILayout.EndHorizontal();
 }
 GUILayout.EndVertical();
 }