Hi Apos,
as far as I remember Visforms is not working with the cache plugin at all. It is not only the error message you receive but even if I change the code, that Visforms does no longer perform the check for doublicate submisssion and this error message is no longer displayed user inputs are not submitted properly.
Feel free to try. The code which produces the error message is located in components/com_visforms/controller.php in the function send() at about line 191
Code:
if (isset( $_SESSION['vis_send_once'.$visform->id])) {
unset($_SESSION['vis_send_once'.$visform->id]);
} else {
JError::raiseWarning( 0, JText::_( "COM_VISFORMS_CAN_SENT_ONLY_ONCE" ));
return false;
}
You can just remove it.
I don't know whether there maybe is a thridparty cache extension, which can help you with the problem.
But please, if you find a solution, share it here.
Kind Regards,
Aicha