It is this site:

http://www.analystnotes.com/user_login.php

after logging in, the right click is blocked.

(for your testing, I just registered an account. name: aaaabbbb, password: aaaa1111)

I tried this script, but it didn't work.

http://userscripts.org/scripts/show/11694

Please help. Thank you very much!

Disable javascript :)
Install web developer or noscript or javascript options or another addons that can disable javascript

Strange, but I didn't experience context menu blocking on that site.
Anyway, you can prevent it by clearing corresponding checkbox in options->content->"advanced" next to "enable javascript".