Hi,
Several bugs have been reported with characteristics with Joomla 3.4 due to the way the popup system has been modified in that version of Joomla.
We've patched HikaShop since then in order to fix the different issues.
For example:
www.hikashop.com/support/forum/product-c...cs-error/193546.html
The best is that you download again the HikaShop install package from our website and install it on your website. It contains the several fixes that we added in the last few days so that it works properly with the new version of Joomla.