无法处理InvalidCastException以使C＃在VB6中使用

Question

我想要实现的目标是将旧的VB6代码慢慢模块化为C＃ 我在VB6中创建一个测试来按下一个按钮并执行我的c＃表单并传回一个字符串值 我昨天有工作，某种方式改变了，它不再有效。以下是我遇到问题的C＃代码。

#define USE_COM

using System;
using System.Linq;
using System.Windows.Forms;

namespace CMS_DB_Operator_Input
{
    static class Program
    {
        /// <summary>
        /// Open the OperatorInput Form
        /// 
        /// Note: Will output the result to console out on success
        /// </summary>
        /// <param name="args">0: The Default Filter to Use</param>
        /// <returns>
        ///     0: Failure to Select
        ///     1: Successfully Selected an Item
        /// </returns>
        [STAThread]
        static int Main(string[] args)
        {
            Application.EnableVisualStyles();
            Application.SetCompatibleTextRenderingDefault(false);

            string displayName = (args.Length > 1) ? args[1] : null;
            string result = "";
            displayName = "CBU35PN42";
            //displayName = "";

#if USE_COM
            CMS_DB_GateKeeper.IGateKeeperUI api = new MS_DB_GateKeeper.GateKeeperUI();
            result = api.AskOperatorInput(displayName); // <- INVALID CAST EXCEPTION was unhandled
#else
            CMS_DB_GateKeeper.CMS_DB_GateKeeper_OperatorInput op = new CMS_DB_GateKeeper.CMS_DB_GateKeeper_OperatorInput(displayName);
            if (displayName == null)
            {
                Application.Run(op);
                if (op.SelectedDisplayName != null)
                {
                    result = op.GetXmlResult(op.SelectedDisplayName); // Success
                }
            }
            else
            {
                result = op.GetXmlResult(displayName);
            }
#endif
            Console.WriteLine(result);

            return 0; 
        }
    }
}