Hello,
What version of Core plugin do you use? In case it is 1.5.3 version, you need to update XStore theme to 6.2.3 version http://xstore.helpscoutdocs.com/article/63-theme-update If the theme and Core have compatible versions, according to information from our changelog – https://xstore.8theme.com/update-history/ , provide temporary wp-admin and FTP access.
Regards
