Hi,
In order to avoid such kind of issue, the next HikaShop release will display the error message in the red box ; but with the current release, you need to open the browser inspector to get the content returned by the Ajax upload.
We know that it is not simple ; that's why we worked on some improvements to directly display an understandable error message in the red box.
Regards,
Jerome - Obsidev.com
HikaMarket & HikaSerial developer / HikaShop core dev team.
Also helping the HikaShop support team when having some time or couldn't sleep.
By the way, do not send me private message, use the "contact us" form instead.