Cannot update quantity manually / undefined

Hello, I am using latest Joomla 3 and Virtuemart, I have updated storefront template to latset version, but in category view, I cannot manually update quantity , whenever I try to insert a number, "undefined" is displayed. + and - buttons seem to work, though its essential to have this feature.
I have searched virtuemart forums, but no solution about this.
Thanks in advance

Could you please provide me with a URL to your website, either here or via PM (click the “Private Message” text underneath my avatar) so that I may analyze it? It is a lot easier for us to diagnose issues when we have a live site to examine.