private static object GetInstance(string CacheKey)        {            object objType = DataCache.GetCache(CacheKey);            if (objType ==null)            {                try                {                    objType = Assembly.Load(DALFactory._path).CreateInstance(CacheKey);                    DataCache.SetCache(CacheKey, objType);                }                catch (Exception ex)                {                    throw ex;                }            }            return objType;        }     中的objType = Assembly.Load(DALFactory._path).CreateInstance(CacheKey);objType怎么為null 啊 DALFactory._path和CacheKey都有值 怎么Assembly.Load沒有用啊