In order to fix the problem, please contact us via Client Area. Problem occurs due to incorrect session handling in PrestaShop CMS.
PrestaShop - session cleaning error
When you try to clear session data in PrestaShop, the CMS tries to clear the contents of the default session directory that does not have full access rights. That's why this error occurs during cleaning. The solution is to change the directory where the sessions are stored. After reporting the problem via Client Area, our support will solve this problem for You.