WCF程序在一台服务器上的行为很奇怪-为什么?

我为sharepoint提供了一个简单的get list方法(SharePointList是list.asmx的webreference)。

    /// <summary>
    /// Returns a list of sharepoint lists
    /// </summary>
    /// <returns>A list of sharepoint lists</returns>
    private string GetSharePointLists()
    {     
        StringBuilder stringBuilder = new StringBuilder();
        try
        {

            SharePointList.ListsSoapClient proxy = new SharePointList.ListsSoapClient();
            proxy.ClientCredentials.Windows.ClientCredential = new NetworkCredential();
            XmlElement lists = proxy.GetListCollection();
            var q = from c in lists.ChildNodes.Cast<XmlNode>()
                    select new
                    {
                        DefaultViewUrl = c.Attributes["DefaultViewUrl"].Value,
                        Title = c.Attributes["Title"].Value
                    };

            foreach (var x in q)
            {
                stringBuilder.AppendLine(string.Format("{0} http://REMOVED/{1}", x.Title, x.DefaultViewUrl.Replace(" ", "%20")));
            }
        }
        catch (Exception ex)
        {
            throw new Exception(ex.ToString());
        }
        return stringBuilder.ToString();
    }

HTTP请求未经客户端身份验证方案“Ntlm”授权。从服务器接收的身份验证标头为“NTLM”。

有人知道这里发生了什么,怎么解决吗?