Hello,
That message indicate that the product alias is empty or contain the value that another product is using too.
Please provide steps that you made in order to have that message ; you're talking about "copying" a product but you do not provide details about it.
And please note that HikaShop product can have multiple categories, you do not need to copy a product to display it in different categories ; copying is just a way to gain time by duplicate the product content (and some fields must need to be modified afterwards, like the product code, alias...).
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.