This usually happens when a user has adjusted the security settings on their browser.
In Chrome, navigate to the advanced settings. Check 'Allow local data to be set', and uncheck 'Block third-party cookies and site data'.
In Safari, navigate to Privacy & Security. Select the option under Cookies to 'Allow from websites I visit.'You can also try using a different browser.
If adjusting your browser settings to allow cookies does not work, please contact us at email@example.com.