"error updating cart" Problem

[n2o37]

Hi,

I'm new of the forum and joomla, and I read this topic http://forum.virtuemart.net/index.php?topic=132491.0 but I can't find the way to fix the problem.
The problem is the same (refresh/delete product quantity, accept terms, etc.) and maybe I don't know where I have to put hand!

Please, help me!

I use:
VirtueMart 3.0.18
Joomla! 3.6.4

Thank you!