ArgumentOutOfRangeException: Help?

I'm getting this error : ArgumentOutOfRangeException: Index is less than 0 or more than or equal to the list count.

in response to:

var card : Object = gridArray[i][j];

in:

 GUILayout.BeginVertical();
 GUILayout.FlexibleSpace();
 
 for(var i=0; i<rows;i++)
 {
     GUILayout.BeginHorizontal();
     GUILayout.FlexibleSpace();
     for(var j=0; j<columns;j++)
         {
             var card : Object = gridArray[i][j];
             
             if(GUILayout.Button(Resources.Load(card.img),GUILayout.Width(cardWidth)))
             {
                 Debug.Log(card.img);
             }
         }
         GUILayout.FlexibleSpace();
         GUILayout.EndHorizontal();
 }
 GUILayout.FlexibleSpace();
 GUILayout.EndVertical();

does anyone know what's going on? I'm following a tutorials and was kindof hoping that the code would be bug free but I must have made a mistake somewhere.