什么可能导致asp.net网站“服务不可用”不时？

My site works well sometime, but after the recent update, the customer reported that it will be "service unavailable" from time to time. I encountered this before, as I also upload the source .cs code and resource file to IIS, so if the .cs changes, the server will rebuild the application and in this time, every client request will be returned as "service unavailable".My site works well sometime, but after the rece