I've fixed the site search from the main toolbar. If you went directly to the search page, it worked, but not from the toolbar. This was due to a Drupal upgrade applied late last night to fix a security vulnerability. In the process, it changed the way forms work (with tighter validation). The custom theme used by the site didn't have this validation applied, so Drupal was rejecting anything you entered. I've updated the theme to work with the new validation.
Long story short: you can use the search box again.