Hi,
The line 21 of the class user in HikaShop 1.6.0 is
if(empty($data[$type.'_'.$id])){
I am really sure that it can't be the source of the problem except if the class as been modified.
Did you modified this file ? What do you have in the line 21 of your class user file ?
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.