weird 404 error

[wworange]

Dear Support:

One client said that he got a 404 error page.
URL "http:///www.domain.com/images/xxx.pdf"
I ssh to the server and found xxx.pdf consist in the right position.
I can access to "http://myserver's IP/~user/images/xxx.pdf"
But got a 404 page from "http://www.domain.com/images/xxx.pdf"
I chmod -R 777 images/ and got the same
Weird.I cp xxx.pdf ..(under the public_html) "http://www.domain.com/xxx.pdf" It can display normally.
BTW.All of other setup is default

Regards,