Sprout Form submit: The CSRF token could not be verified! I have a form created by Sprout Forms, which results in an error when submitted:

The CSRF token could not be verified!

Here is the log:

2016/06/09 11:06:17 [error] [exception.Craft\HttpException.400] exception 'Craft\HttpException' with message 'The CSRF token could not be verified.' in /home/forge/www.fira.co.uk/craft/app/services/HttpRequestService.php:1314
Stack trace:
#0 /home/forge/www.fira.co.uk/craft/app/framework/base/CComponent.php(561): Craft\HttpRequestService-&gt;validateCsrfToken(Object(CEvent))
#1 /home/forge/www.fira.co.uk/craft/app/framework/base/CApplication.php(212): CComponent-&gt;raiseEvent('onBeginRequest', Object(CEvent))
#2 /home/forge/www.fira.co.uk/craft/app/framework/base/CApplication.php(183): CApplication-&gt;onBeginRequest(Object(CEvent))
#3 /home/forge/www.fira.co.uk/craft/app/index.php(62): CApplication-&gt;run()
#4 /home/forge/www.fira.co.uk/public/index.php(19): require_once('/home/forge/www...')
#5 {main}
REQUEST_URI=/publications/industry-statistics
HTTP_REFERER=http://www.fira.co.uk/publications/industry-statistics
The form code in the template was wrapped in a {% cache %} tag.