404 error in popup after adding product to cart

-- HikaShop version -- : 2.5.0
-- Joomla version -- : 2.5
-- Error-message(debug-mod must be tuned on) -- : 404 error

After upgrading to latest hikashop version, I have a 404 error in the popup message after adding products to the cart.

I did switch off SEF and caching, but the error did NOT disappear.
Only change I did was the update to the latest Hikashop version.

Before this was working.

Please advise what to do

Thanks and best regards

Please look here: www.hikashop.com/forum/product-category-...update-to-2-5-0.html