使用arr过程中遇到诡异的502错误，把承载arr的网站的应用程序池切换为.NET2.0，则可能解决这个问题，目前原因不详
参见官方论坛
http://forums.iis.net/t/1187225.aspx/1?ARR+POST+requests+causing+502+3+timeouts
UPDATE: further testing reveals that there seems to be an issue if the main server is running as a .NET 4.0 application. I created a dummy site with a single Default.html document and setup a reverse proxy for myserver.com/Forum. If the dummy site is configured as a .NET 4.0 application then the POST body does not always make it past ARR. However, if I configured the dummy site as .NET 2.0 then everything works fine. I can toggle the dummy site's application pool from ASP.NET 4.0 to ASP.NET 2.0 and it goes from broken to working.