ActionNotSupported error

Hi
I am getting the following error when I try to run my WCF service in
the browser:
http://localhost:8000/DITService/DITService

<s:Envelope xmlns:s="http://schemas.xmlsoap.org/soap/envelope/">
- <s:Body>
- <s:Fault>
<faultcode xmlns:a="http://schemas.microsoft.com/ws/2005/05/
addressing/none">a:ActionNotSupported</faultcode>
<faultstring xml:lang="en-US">The message with Action '' cannot be
processed at the receiver, due to a ContractFilter mismatch at the
EndpointDispatcher. This may be because of either a contract mismatch
(mismatched Actions between sender and receiver) or a binding/security
mismatch between the sender and the receiver. Check that sender and
receiver have the same contract and the same binding (including
security requirements, e.g. Message, Transport, None).</faultstring>
</s:Fault>
</s:Body>
</s:Envelope>

My service us declared thus:

using System;
using System.Collections.Generic;
using System.Text;
using System.ServiceModel;
using System.Runtime.Serialization;
using MVCShell;
using DITDataAccessLayer;
using System.Data;

namespace DITService
{

[ServiceContract()]
public interface IDITService
{
[OperationContract]
DataSet LoadCatalog(string entityType);
}

public class DITServiceType : IDITService
{
#region IDITService Members

DataSet IDITService.LoadCatalog(string entityType)
{
CatalogLoader cl = new CatalogLoader();
DataSet catDs = cl.LoadCatalog(entityType, Guid.Empty);
return catDs;
}

#endregion
}
}

My client App.Config is thus:
<?xml version="1.0" encoding="utf-8"?>
<configuration>
<system.serviceModel>
<bindings>
<basicHttpBinding>
<binding name="BasicHttpBinding_IDITService"
closeTimeout="00:01:00"
openTimeout="00:01:00" receiveTimeout="00:10:00"
sendTimeout="00:01:00"
allowCookies="false" bypassProxyOnLocal="false"
hostNameComparisonMode="StrongWildcard"
maxBufferSize="65536" maxBufferPoolSize="524288"
maxReceivedMessageSize="65536"
messageEncoding="Text" textEncoding="utf-8"
transferMode="Buffered"
useDefaultWebProxy="true">
<readerQuotas maxDepth="32" maxStringContentLength="8192"
maxArrayLength="16384"
maxBytesPerRead="4096" maxNameTableCharCount="16384" />
<security mode="None">
<transport clientCredentialType="None"
proxyCredentialType="None"
realm="" />
<message clientCredentialType="UserName"
algorithmSuite="Default" />
</security>
</binding>
</basicHttpBinding>
</bindings>
<client>
<endpoint address="http://localhost:8000/DITService/DITService"
binding="basicHttpBinding"
bindingConfiguration="BasicHttpBinding_IDITService"
contract="IDITService" name="BasicHttpBinding_IDITService" / </client>
</system.serviceModel>
</configuration>

Anyone know why I am getting this error?

thanks,

Arun