邮件推送时，本地调试和国内服务器上都没问题，但在香港服务器会报错GetAcsResponse

在用邮件推送功能时，在本地调试和国内服务器上都没有问题，但在香港服务器上跑就会报错：

调用这句时，抛出异常： SingleSendMailResponse httpResponse = client.GetAcsResponse(request);

请问大家是哪里的问题？ 用的AccessKey等都是一样，没有问题。

抛出异常：

[XPathException: 表达式的计算结果必须为节点集。] MS.Internal.Xml.XPath.XPathParser.ParseNodeTest(AstNode qyInput, AxisType axisType, XPathNodeType nodeType) +582 MS.Internal.Xml.XPath.XPathParser.ParseStep(AstNode qyInput) +346 MS.Internal.Xml.XPath.XPathParser.ParseRelativeLocationPath(AstNode qyInput) +27 MS.Internal.Xml.XPath.XPathParser.ParsePathExpr(AstNode qyInput) +226 MS.Internal.Xml.XPath.XPathParser.ParseUnionExpr(AstNode qyInput) +27 MS.Internal.Xml.XPath.XPathParser.ParseMultiplicativeExpr(AstNode qyInput) +29 MS.Internal.Xml.XPath.XPathParser.ParseAdditiveExpr(AstNode qyInput) +29 MS.Internal.Xml.XPath.XPathParser.ParseRelationalExpr(AstNode qyInput) +29 MS.Internal.Xml.XPath.XPathParser.ParseEqualityExpr(AstNode qyInput) +29 MS.Internal.Xml.XPath.XPathParser.ParseAndExpr(AstNode qyInput) +27 MS.Internal.Xml.XPath.XPathParser.ParseOrExpr(AstNode qyInput) +27 MS.Internal.Xml.XPath.XPathParser.ParseExpresion(AstNode qyInput) +32 MS.Internal.Xml.XPath.XPathParser.ParseXPathExpresion(String xpathExpresion) +78 System.Xml.XPath.XPathExpression.Compile(String xpath, IXmlNamespaceResolver nsResolver) +61 System.Xml.XPath.XPathNavigator.Select(String xpath) +18 System.Xml.XmlNode.SelectNodes(String xpath) +75 Aliyun.Acs.Core.Reader.XmlReader.Read(XmlNode element, String path, Boolean appendPath) +167 Aliyun.Acs.Core.Reader.XmlReader.Read(XmlNode element, String path, Boolean appendPath) +566 Aliyun.Acs.Core.Reader.XmlReader.Read(String xml, String endpoint) +177 Aliyun.Acs.Core.DefaultAcsClient.ReadError(AcsRequest1 request, HttpResponse httpResponse, Nullable1 format) +154 Aliyun.Acs.Core.DefaultAcsClient.ParseAcsResponse(AcsRequest`1 request, HttpResponse httpResponse) +229 Tunynet.Common.ValidateCodeService.EmailSend(IUser user, String subject, MailMessage model, Boolean change, String newEmailAddress)