Form saying unavailable on website

Hi our form "home security application form" is not working when the form is completed at http://www.justicesecurity.co.uk/home-security-installation-request-form.html when the form is submitted the error message "This form is currently unavailable" however all the other forms on our site work ok

any ideas

I see that the form is set to receive only 20 submissions and notice that you have received 20 submissions for this JotForm. If you want to change the submissions limit, you can change it from Form Preferences.

Hope this information helps!!