WebService 在传回 ArrayList 时说： XML 文档时出错

System.InvalidOperationException: 生成 XML 文档时出错。 ---> System.InvalidOperationException: CProxyTypeSpace_EntityRoleEntity_NHibernate_ProxyINHibernateProxy_System_Runtime_SerializationISerializable2 无法序列化，因为它没有无参数的构造函数。   在 System.Xml.Serialization.TypeDesc.CheckSupported()   在 System.Xml.Serialization.TypeScope.GetTypeDesc(Type type, MemberInfo source, Boolean directReference, Boolean throwOnError)   在 System.Xml.Serialization.XmlSerializationWriter.CreateUnknownTypeException(Type type)   在 System.Xml.Serialization.XmlSerializationWriter.WriteTypedPrimitive(String name, String ns, Object o, Boolean xsiType)   在 Microsoft.Xml.Serialization.GeneratedAssembly.XmlSerializationWriter1.Write1_Object(String n, String ns, Object o, Boolean isNullable, Boolean needType)   在 Microsoft.Xml.Serialization.GeneratedAssembly.XmlSerializationWriter1.Write6_ArrayOfAnyType(Object o)   在 Microsoft.Xml.Serialization.GeneratedAssembly.ArrayListSerializer.Serialize(Object objectToSerialize, XmlSerializationWriter writer)   在 System.Xml.Serialization.XmlSerializer.Serialize(XmlWriter xmlWriter, Object o, XmlSerializerNamespaces namespaces, String encodingStyle, String id)   --- 内部异常堆栈跟踪的结尾 ---   在 System.Xml.Serialization.XmlSerializer.Serialize(XmlWriter xmlWriter, Object o, XmlSerializerNamespaces namespaces, String encodingStyle, String id)   在 System.Xml.Serialization.XmlSerializer.Serialize(TextWriter textWriter, Object o)   在 System.Web.Services.Protocols.XmlReturnWriter.Write(HttpResponse response, Stream outputStream, Object returnValue)   在 System.Web.Services.Protocols.HttpServerProtocol.WriteReturns(Object[] returnValues, Stream outputStream)   在 System.Web.Services.Protocols.WebServiceHandler.WriteReturns(Object[] returnValues)   在 System.Web.Services.Protocols.WebServiceHandler.Invoke()