public string Hash(ItemIdentifier itemId)
        {
            //encrypt login and password
            string loginName = "";
            string pass = "";
            getloginAndPass(UserId, ref loginName, ref pass);
            string _url = getWSUrl(this.Url);

            RepositoryWebservice repo = new RepositoryWebservice(_url);
            repo.Credentials = new System.Net.NetworkCredential(loginName, pass);

            string hash = string.Empty;
            try
            {
                hash = repo.GetItemHash(this.SessionKey, itemId, loginName, pass);
            }
            catch { }

            repo.Dispose();

            return hash;
        }