Hi,
" You cannot access the private section of this site." is a Joomla message and it's not provided by HikaShop.
Please check your Joomla settings and yes, HikaShop use the Joomla accounts (so the Joomla login).
But your current issue is not related to HikaShop for what I can see regarding the "error message".
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.