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STEPS TO REPLICATE:
1 Open the website
2 Click on login with facebook
RESULT It pops up a message written 'undefined error'.
EXPECTED RESULT user login. However, if you open the browser again. it shows that is logged.
BROWSER Chrome / IE
Did you modify htaccess before? because on FB connection action I get error 303 which this issue usually caused by htacess configuration, since I also see two SEO and SEF component on your backend.