Error 500 with message error

[Lelouch]

Hello,

Sorry in advance for my english. I'm a french guys. ^^

VirtueMart 3.0.18
Joomla 3.6.5

In my website, when I click on the cart shop, my page is white with error 500.

I enabled debugging messages and the message is :
- Fatal error: Access level to VirtueMartViewCart::$useSSL must be public (as in class VmView) in plugins/system/vponepagecheckout/cart/cartview.html.php on line 19

But on line 19 there is :
class VirtueMartViewCart extends VmView

SSL isn't activate in my configuration.

I am an amateur, if you could help. I searched in the forum without success.

Thanks.

Lelouch

Edit :
Answer :

In the file, search :
protected $useSSL;

Change to :
public $useSSL;

SOLVED.