关于Webservice的一个有关问题

关于Webservice的一个问题
  public class ContactSyncService : System.Web.Services.WebService
    {
        [WebMethod]
        [SoapHeaderAttribute("SecurityHeaderValue")]
        [SoapDocumentMethodAttribute("", Use = SoapBindingUse.Literal, ParameterStyle = SoapParameterStyle.Bare)]
        [return: System.Xml.Serialization.XmlElementAttribute("MapChangesResponse", Namespace = "http://msg.pim.vnet.cn")]
        public webservice.MapChangesResponse MapChanges(webservice.SecurityHeader SecurityHeader, webservice.MapChangesRequest MapChangesRequest)
        {
            object[] results = new object[] {
                        SecurityHeader,
                        MapChangesRequest};
            return ((webservice.MapChangesResponse)(results[0]));
        }


        [WebMethod]
        [SoapHeaderAttribute("SecurityHeaderValue")]
        [SoapDocumentMethodAttribute("", Use = SoapBindingUse.Literal, ParameterStyle = SoapParameterStyle.Bare)]
        [return: System.Xml.Serialization.XmlElementAttribute("SyncChangesResponse", Namespace = "http://msg.pim.vnet.cn")]
        public webservice.SyncChangesResponse SyncChanges(webservice.SecurityHeader SecurityHeader, webservice.SyncChangesRequest SyncChangesRequest)
        {
            object[] results = new object[] {
                        SecurityHeader,
                        SyncChangesRequest};
            return ((webservice.SyncChangesResponse)(results[0]));
        }

        [WebMethod]
        [SoapHeaderAttribute("SecurityHeaderValue")]
        [SoapDocumentMethodAttribute("", Use = SoapBindingUse.Literal, ParameterStyle = SoapParameterStyle.Bare)]
        [return: System.Xml.Serialization.XmlElementAttribute("NotificationResponse", Namespace = "http://msg.pim.vnet.cn")]
        public webservice.NotificationResponse Notification(webservice.SecurityHeader SecurityHeader, webservice.Param[] NotificationRequest)
        {
            object[] results = new object[] {
                        SecurityHeader,

                        NotificationRequest};
            return ((webservice.NotificationResponse)(results[0]));
        }
        
    }
到运行页面的时候就出现System.Exception: 头属性/字段 ContactSyncService.SecurityHeaderValue 缺失或者不是公共的。这个错误，请问是什么原因？？

[解决办法]
ding
[解决办法]
你是怎么解决的啊？