WCF "endpoint not found" error (404 0 0)

I am stuck by a very strange WCF problem on one of my asp.net website. The service returns "endpoint not found" error for only one type of service request. For instance:

It works fin开发者_运维知识库e for http://www.stackoverflow.com/main/UpdateService.svc/books/

but return "endpoint not found" error for http://www.stackoverflow.com/main/UpdateService.svc/users/

What's more strange is if I build a debug version, and deploy it to a "Dev" asp.net website. Both http://www.stackoverflow.com/Dev/UpdateService.svc/books/ and http://www.stackoverflow.com/Dev/UpdateService.svc/users/ work fine.

I have spent lots of time on the problem but still no luck with it. I looked the iis log files, the error code is "404 0 0 468".