We recommend all existing VM 3 users of the plugin to install the latest update in their sites before updating VirtueMart component above 3.0.9 to avoid any problem.
Alternatively if you are not in a position to update the plugin immediately then you can make the following changes in your site.
Find the following codes in line 919:
Replace above by:
$this->cart->_dataValidated = true;
$this->cart->_dataValidated = method_exists($this->cart, 'getCartHash') ? $this->cart->getCartHash() : true;
The above change will take care of the security checking change introduced since VM 220.127.116.11. However we always recommend that you update the complete plugin and remain updated with all latest changes in VirtueMart.