I had the same problem, form validation was not working and after submitting the arrow continues spinning indefinitely. However email would arrive. The only plugin I installed after Contact form was working was Akismet, disabled it did not help, and I upgraded to newer version of WordPress now 3.0, contact form is version is 2.4.2.
I’m happy t report that for me Simon’s solution (in Cadred’s post above) works.
Once again, add to your contact form in form creation window at the top:
<p style=”visibility:hidden;”>[file upload]</p>
Worked for me ??