When trying to add a product that has already been added, the system sends an error message "You can't add more than {limit_quantity} items for {product_name}."
Why, and where can I set aside this setting to let customers add whatever they want to the cart?

I have just added a product and then again added this same product twice more - when I go to my basket I find three there.
 
Not sure what your problem is, I'm afraid?
 
Chris

You have a setting within ViArt that we can say a customer can only purchase x amount of the product during a certain time-frame or ever. It's under the customer setup.
 
Hope this helps.

You have to be an intrepid explorer with Viart, Dan !!!

Can´t find this setting? It´s what I was looking for, but didn´t find on my own, and don´t find now either..

My error... I mistakenly told you where you would limit the max/min COST of the order. The actual setting for the limitation of the product(s) would be in each product under the 'Stock/Shipping' tab. Look where it says:
 
Minimum Quantity [] (minimum allowed number of items to purchase)
Maximum Quantity [] (maximum allowed number of items to purchase)
 
Hope this helps.