Error when increasing product quantity

Hello
Using Joomla 3.4.0, Storefront 3.16 and Virtuemart 3.0.6.2
When I try and use the + or - button to increase products before adding to cart I see a 'NaN' in the quantity box and receive the following error: You can buy this product only in multiples of 1 pieces!

It's seems every time I get one problem fixed with virtuemart 3 and the storefront template I come across a new one! Can anyone offer any suggestions on how to fix this issue as I really need to get this site live.

Many thanks
Emily

Hello,

First of all - are you sure that all VM override files are properly updated? Because as I remember I've fixed this kind of issue in v.3.16

Thank you so much - you were right. I've replaced the VM override files again and all is working