IllegalArgumentException when invoking axis2-webservice with client

i just wrote a webservice using the axis2-framework .. the service can
be found here:
---------------------------------------------------
package de.testService;

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.util.Vector;

public class TestService {

     public Connection con = null;
     TransportContainer tc = new TransportContainer();
     Vector v = new Vector();

     public final void connection() throws Exception {
         Class.forName("com.mysql.jdbc.Driver");
         con = DriverManager.getConnection(
                 "jdbc:mysql://localhost:3306/travelagent", "root", "");
     }

     public TransportContainer getHotels(String table) {
         try {
             connection();
             String sql = "SELECT * FROM " + table;
             PreparedStatement pStmt = con.prepareStatement(sql);
             ResultSet rs = pStmt.executeQuery();
             while (rs.next()) {
                 v.addElement(new Hotel(rs.getString(2), rs.getString(3), rs
                         .getString(4), rs.getString(6), rs.getInt(5)));
             }
         } catch (Exception e) {
             e.printStackTrace();
         }
         tc.setData(v);
         return tc;

     }

}
---------------------------------------------------

the service uses a class called TransportContainer, which contains the
data that should be send from the service to the client. this class can
be found here:

---------------------------------------------------
package de.testService;

import java.util.Vector;

public class TransportContainer {

     public TransportContainer() {

     }

     public Vector v;

     public void setData(Vector data) {
         this.v = data;
     }

     public Vector getData() {
         return this.v;
     }
}
---------------------------------------------------

to invoke the service, i wrote a client which can be found here:

---------------------------------------------------
package de.wsTester;

import javax.xml.namespace.QName;

import org.apache.axis2.AxisFault;
import org.apache.axis2.addressing.EndpointReference;
import org.apache.axis2.client.Options;
import org.apache.axis2.rpc.client.RPCServiceClient;

import de.testService.*;

public class TestClient {

     public static void main(String[] args) throws AxisFault {

         RPCServiceClient sender = new RPCServiceClient();
         Options options = sender.getOptions();

         EndpointReference targetERP = new EndpointReference(
                 "http://localhost:8080/axis2/services/testService");
         options.setTo(targetERP);

         QName opGetHotels = new QName("http://testService.de",
"getHotels");

         String table = "hotels";
         Object[] opArgs = new Object[] { table };

         Class[] returnTypes = new Class[] { TransportContainer.class };
         Object[] response = sender.invokeBlocking(opGetHotels,
opArgs,returnTypes);
     }

}
---------------------------------------------------

when i start the client, i get the following exception:

---------------------------------------------------
Exception in thread "main" java.lang.IllegalArgumentException: argument
type mismatch
     at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
     at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
     at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
     at java.lang.reflect.Method.invoke(Unknown Source)
     at
org.apache.axis2.databinding.utils.BeanUtil.deserialize(BeanUtil.java:391)
     at
org.apache.axis2.databinding.utils.BeanUtil.processObject(BeanUtil.java:655)
     at
org.apache.axis2.databinding.utils.BeanUtil.ProcessElement(BeanUtil.java:603)
     at
org.apache.axis2.databinding.utils.BeanUtil.deserialize(BeanUtil.java:535)
     at
org.apache.axis2.rpc.client.RPCServiceClient.invokeBlocking(RPCServiceClient.java:103)
     at de.wsTester.TestClient.main(TestClient.java:29)
---------------------------------------------------

thx to soapmonitor, i can see that the service return the expected
data-structure

---------------------------------------------------
<?xml version='1.0' encoding='utf-8'?>
<soapenv:Envelope xmlns:soapenv="http://schemas.xmlsoap.org/soap/envelope/">
   <soapenv:Body>
     <ns:getHotelsResponse xmlns:ns="http://testService.de">
       <ns:return xmlns:ax21="http://testService.de/xsd"
type="de.testService.TransportContainer">
         <ax21:data type="de.testService.Hotel">
           <ax21:hotelCity>MLnchen</ax21:hotelCity>
           <ax21:hotelCode>AX001</ax21:hotelCode>
           <ax21:hotelName>Axis2 Grand Hotel</ax21:hotelName>
           <ax21:numOfStars>5</ax21:numOfStars>
         </ax21:data>
         <ax21:data type="de.testService.Hotel">
           <ax21:hotelCity>Hamburg</ax21:hotelCity>
           <ax21:hotelCode>AX010</ax21:hotelCode>
           <ax21:hotelName>Axis2 Plaza</ax21:hotelName>
           <ax21:numOfStars>4</ax21:numOfStars>
         </ax21:data>
         <ax21:data type="de.testService.Hotel">
           <ax21:hotelCity>Unterammergau</ax21:hotelCity>
           <ax21:hotelCode>AX050</ax21:hotelCode>
           <ax21:hotelName>AchsenhLtte</ax21:hotelName>
           <ax21:numOfStars>1</ax21:numOfStars>
         </ax21:data>
       </ns:return>
     </ns:getHotelsResponse>
   </soapenv:Body>
</soapenv:Envelope>
-------------------------------------------------

whats wrong with my code? i would be thankful for any advice or hints on
how to improve my code.

greetings,

matthias :):)