iis 7 asp.net ajax post 请求字节过大报错问题解决办法

遇到一个ajax post 提交新闻资讯类的文章，报

{"Message":"There was an error processing the request.","StackTrace":"","ExceptionType":""}
firebug 调试及测试发现是post的字节过长。找了好久，终于找到调整配置的解决方案

<appSettings>

<add key="aspnet:MaxJsonDeserializerMembers" value="150000" />
  </appSettings>

<system.web.extensions>
    <scripting>
      <webServices>
        <jsonSerialization maxJsonLength="2147483644"/>
      </webServices>
    </scripting>
  </system.web.extensions>