In WordPress 3.0.x, there is no problem.
In WordPress 3.x, there is the following error in same server.
1. Input Form data
2. Click "Submit" button
3. The process is running, but it cannot finish.
I tried to install "Contact Form to DB Extension".
In "3" item, it cannot finish, but the submitted data sent to this DB.
I checked the processing data using Firebug in Firefox.
As a result:
POST http://******/wordpress/page_id=66 500 Internal Server Error