Hi,
I'm sorry but we do not have any "Class ... does not exist" message in HikaShop (or HikaMarket).
I see that you have a notice from your system plugin "jvnewsletter" ; please be sure that this plugin is not pushing the Joomla error message (or another plugin).
Regards,
PS : I think you're using HikaShop 2.4.0 ; HikaShop 2.4.1 has not been released, yet.
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.