I don't know which template. You really need to go through your edited templates in the style - they will be in red - and do a View History and then Compare your template to the default Jelsoft template and see where you are missing a securitytoken. The other option is that it is from a modification - turn them off and see if you still get the problem. If you still get the problem with them off, then it is your template. If you don't get the problem when they are off, then it is a plugin.
Note: To temporarily disable the plugin system, edit config.php and add this line right under <?php
PHP Code:
define('DISABLE_HOOKS', true);