WCF Serialization Error Using NetTCP -

using vs2012 , nettcpbinding. getting following error when call servicecontract client - service hosted in iis:

there error while trying serialize parameter cs.servicecontracts.zzzzzz.common:getzipcodesresult. innerexception message 'type 'system.delegateserializationholder+delegateentry' data contract name 'delegateserializationholder.delegateentry:http://schemas.datacontract.org/2004/07/system' not expected. consider using datacontractresolver or add types not known statically list of known types - example, using knowntypeattribute attribute or adding them list of known types passed datacontractserializer.'. please see innerexception more details.

here servicecontract:

  [servicecontract(sessionmode = sessionmode.allowed, namespace = "cs.servicecontracts.zzzzzz.common",     name = "izzzzzzcommonservice")] public interface izzzzzzcommonservice {     [operationcontract]     getzipcodesresponse getzipcodes(getzipcodesrequest request); } 

here datacontract:

[datacontract] [serializable] public class getzipcodesresponse : responsebase {     [datamember(isrequired = true)]     public list<zipcodes> zipcodes { get; set; } } 

and here responsebase:

[datacontract] [serializable] [knowntype(typeof(getzipcodesresponse)), xmlinclude(typeof(getzipcodesresponse))] public class responsebase {     [datamember(isrequired = true)]     public int responsecode { get; set; }      [datamember(isrequired = false)]     public int reasoncode { get; set; }      [datamember(isrequired = false)]     public string reasontext { get; set; } } 

here implementation of servicecontract interface:

public class zzzzzzcommonservice : izzzzzzcommonservice {  public getzipcodesresponse getzipcodes(getzipcodesrequest request)     {         var response = new getzipcodesresponse();         try         {             response.zipcodes = zipcodes.getcustom(request.zipcode, request.city, request.state);          }         catch (exception ex)         {             this.buildexceptionresponse(response, ex);         }          return response; // line ok, here error occurs     } } 

and here client code calling service:

 public void zipcodes()     {         var endpoint = new endpointaddress(             "net.tcp://localhost/cs.webservice.zzzzzz.common/zzzzzzcommonservice.svc");          var binding = new nettcpbinding { transfermode = transfermode.buffered, sendtimeout = timespan.maxvalue, receivetimeout = timespan.maxvalue, maxreceivedmessagesize = 100000000, maxbuffersize = 100000000 };          using (var channel = new channelfactory<izzzzzzcommonservice>(binding, endpoint))         {             try             {                 channel.endpoint.contract.sessionmode = sessionmode.allowed;                  var proxy = channel.createchannel();                 var request = new getzipcodesrequest();                  request = new getzipcodesrequest { zipcode = "32701" };                 response = proxy.getzipcodes(request);             }         }     } 

i have debugged code , getting entity , dataset populated appropriate rows when sends dataset when errors.

not sure missing. believe have servicecontract , datacontract members decorated correctly not sure why having problems serializing list.

the problem zipcode class. entity class , not able serialized. deconstructed class , able send client.