有关于WebService的问题......Help

我想在Webservice上传一个employee类
   当我把类的属性...信息填充好后在webservice 上调用...返回这样的错误请问是什么原因>>>>System.InvalidOperationException: 生成 XML 文档时出错。 ---> System.NullReferenceException: 未将对象引用设置到对象的实例。
   at ChemExplorer.HR.Employee.get_EnglishName() in d:\my_projects\chemexplorer\chemexplorer\hr_model\employee.cs:line 304
   at Microsoft.Xml.Serialization.GeneratedAssembly.XmlSerializationWriter1.Write1_Employee(String n, String ns, Employee o, Boolean isNullable, Boolean needType)
   at Microsoft.Xml.Serialization.GeneratedAssembly.XmlSerializationWriter1.Write9_Employee(Object o)
   --- 内部异常堆栈跟踪的结尾 ---
   at System.Xml.Serialization.XmlSerializer.Serialize(XmlWriter xmlWriter, Object o, XmlSerializerNamespaces namespaces, String encodingStyle)
   at System.Xml.Serialization.XmlSerializer.Serialize(XmlWriter xmlWriter, Object o, XmlSerializerNamespaces namespaces)
   at System.Xml.Serialization.XmlSerializer.Serialize(TextWriter textWriter, Object o, XmlSerializerNamespaces namespaces)
   at System.Xml.Serialization.XmlSerializer.Serialize(TextWriter textWriter, Object o)
   at System.Web.Services.Protocols.XmlReturnWriter.Write(HttpResponse response, Stream outputStream, Object returnValue)
   at System.Web.Services.Protocols.HttpServerProtocol.WriteReturns(Object[] returnValues, Stream outputStream)
   at System.Web.Services.Protocols.WebServiceHandler.WriteReturns(Object[] returnValues)
   at System.Web.Services.Protocols.WebServiceHandler.Invoke()