I've created a Contact Us page (my-site.com/contact-us/) using contact-form-7 which works fine on my local WordPress install. However, when I try the same form on the online version of the site, it simply hangs.
I checked the http headers using Fiddler and saw that the url being used by the ajax submit is /contact-us/#wpcf7-f1-p15-o1. The error shown by Fiddler is HTTP 400 "Bad Request". There's no server information, so I'm assuming the request doesn't even make it to the server.
Local setup: XAMPP on Windows XP
Online setup: IIS 6.0 on Windows 2003
WordPress version: 2.9.2
Browser: Opera 10.61
Update: I'm using gmail as my smtp server via the WP-Mail-SMTP plugin.