I didn't find any system plugin or other component or a strange combination of settings in HikaShop. So I went in the config and changed the session handler to none instead of database as I remembered that on some servers, that could cause problems. I then tried again to use the account This email address is being protected from spambots. You need JavaScript enabled to view it. and now I don't have the problem either with that account. So it seems to be solved. Could you try on your end and let me know if you still have problems ?
HIKASHOP ESSENTIAL 49,95€The basic version. With the main features for a little shop.
HIKAMARKETAdd-on Create a multivendor platform. Enable many vendors on your website.
HIKASERIALAdd-on Sale e-tickets, vouchers, gift certificates, serial numbers and more!
MARKETPLACEPlugins, modules and other kinds of integrations for HikaShop
HIKAAUCTION 40€Add-on Create auctions and let your customers bid for products.
ACCESS THE CHECKOUTClick here to access the payment area
( why you don't have a pm) 
If i will face any other problem i'be back. Thank you very much 
