<system.web.extensions>
  <scripting>
    <webServices>
      <jsonSerialization>
        <converters>
          <add name="DataSetConverter" type="Microsoft.Web.Preview.Script.Serialization.Converters.DataSetConverter, Microsoft.Web.Preview"/>
          <add name="DataRowConverter" type="Microsoft.Web.Preview.Script.Serialization.Converters.DataRowConverter, Microsoft.Web.Preview"/>
          <add name="DataTableConverter" type="Microsoft.Web.Preview.Script.Serialization.Converters.DataTableConverter, Microsoft.Web.Preview"/>
        </converters>
      </jsonSerialization>
    </webServices>
  </scripting>
</system.web.extensions>
