[Plugin: Participants Database] Validation not working

The plugin is Great!
Form validation is not working on my site, I am using a custom Thank you page BTW.
You can check the form at:
http://www.fanbolero.com/fanbolero-concurso-mercurial-vapor-viii/

If you submit (mandar) with all blank fields, the page returns to the same page without error messages or red border on the fields.

Any ideas?

http://wordpress.org/extend/plugins/participants-database/