using System;

namespace ComInteraction
{
    public interface ITest
    {
        String About { get; }
    }

    public class TestClass : ITest
    {
        public String About
        {
            get
            {
                return "This is TestClass class";
            }
        }

        public string GetString(string val)
        {
            return "This is a val (" + val + ")";
        }

        public string[] GetStrings(string val)
        {
            string[] strings = new string[ 10 ];

            for (int i =  0 ; i <  10 ; i++)
                strings[i] = "This is a val (" + val + ") № " + i;

            return strings;
        }
    }
}

var testObj;
var strBuffer = "123";

testObj = new ActiveXObject("ComInteraction.TestClass");

var string = testObj.GetString(strBuffer);
WshShell.Popup(string); // <---------- Нормально

var strings = testObj.GetStrings(strBuffer);
WshShell.Popup(strings[ 0 ]); // <---------- Ошибка