Eu tenho isso quando eu consome um webservice:

A operação 'Login' do contrato 'IServices' especifica vários parâmetros do corpo da solicitação a serem serializados sem nenhum elemento de wrapper. No máximo, um parâmetro de corpo pode ser serializado sem elementos de wrapper. Remova os parâmetros de corpo extras ou defina a propriedade BodyStyle no WebGetAttribute / WebInvokeAttribute como Wrapped.

Eu uso interface parecido com:

namespace DreamServices
{
    // NOTE: You can use the "Rename" command on the "Refactor" menu to change the interface name "IService1" in both code and config file together.
    [ServiceContract]
    public interface IServices
    {
        [OperationContract]
        [WebInvoke(Method = "GET",
        ResponseFormat = WebMessageFormat.Json,

        BodyStyle = WebMessageBodyStyle.Wrapped,

        UriTemplate = "LogIn/{username}/{password}")]
        string Login(string username, string password);

        [OperationContract]
        [WebInvoke(
            Method = "GET",
            ResponseFormat = WebMessageFormat.Json,
            BodyStyle = WebMessageBodyStyle.Wrapped,
            UriTemplate = "WaletTotalAmount/{userid}")]
        double? WaletTotalAmount(string userid);

        [OperationContract]
        [WebInvoke(
            Method = "GET",
            ResponseFormat = WebMessageFormat.Json,
            BodyStyle = WebMessageBodyStyle.Wrapped,
            UriTemplate = "UserService/{userid}")]
        IList<UserServiceses> UserService(string userid);

        [OperationContract]
        [WebInvoke(Method = "POST",
            ResponseFormat = WebMessageFormat.Json,
            RequestFormat = WebMessageFormat.Json,
            BodyStyle = WebMessageBodyStyle.Wrapped,
            UriTemplate = "InsertUpdateWallet/{userid}/{Amount}/{ComissionAmount}")]
        void InsertUpdateWallet(string userid, string Amount, string ComissionAmount);

    }
}

e eu hospedo, então eu adiciono uma referência web ao meu site e modifico o web.config de tal forma que o será como

<system.serviceModel>

    <behaviors>
      <endpointBehaviors>
        <behavior name="web">
          <webHttp />
          <dataContractSerializer maxItemsInObjectGraph="2147483647"/>
        </behavior>
      </endpointBehaviors>
      <serviceBehaviors>
        <behavior>
          <dataContractSerializer maxItemsInObjectGraph="2147483647" />
          <serviceMetadata httpGetEnabled="true" />
          <serviceDebug includeExceptionDetailInFaults="true" />
        </behavior>
      </serviceBehaviors>
    </behaviors>
    <bindings>
      <webHttpBinding>
        <binding name="defaultRest">
          <readerQuotas maxStringContentLength="2147483647" maxArrayLength="2147483647" maxBytesPerRead="2147483647" maxDepth="64" maxNameTableCharCount="2147483647" />
          <security mode="None" />
        </binding>
      </webHttpBinding>
    </bindings>

    <client>
      <endpoint address="http://localhost:1381/PMAHost/Service.svc" binding="webHttpBinding" contract="ServiceReference.IServices" behaviorConfiguration="web"/>
    </client>

    <serviceHostingEnvironment multipleSiteBindingsEnabled="true" />
  </system.serviceModel>

Alguma idéia de como corrigir esse erro?