A recent update to the Facebook SDK has caused issues with some older versions which causes the following error:
PHP Fatal error: Cannot use object of type stdClass as array in FacebookRedirectLoginHelper.php on line 191
To fix this issue, go to FacebookRedirectLoginHelper.php
then find $response['access_token']
You will see this code:
if (isset($response['access_token'])) { return new FacebookSession($response['access_token']); }
Replace it with this:
if (isset($response->access_token)) { return new FacebookSession($response->access_token); }