Hi,
The drag&drop upload lib allow the "upload by chunk" ; thanks to that your browser can send the big file part by part and HikaShop will recreate the final file in the server.
To do so, it uses the upload limitation in order to determine the chunk size.
Now the "error" you have do not provide the real error message.
Best would be to check in your PHP error log to check if there is no error message.
Afterwards, the best would be to see the "network" in your browser to get the result of the ajax call (which is done to upload the file). By having the returned content, you could have information about the error.
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.