Note that the file requested is "500px.php", while the file on disk is "px500.php".
This can be fixed by renaming the px500.php file to 500px.php, and changing the name of the class defined in that file to match.
Warning: require_once(/data/web/wp-content/plugins/wordpress-social-login/hybridauth/Hybrid/Providers/500px.php): failed to open stream: No such file or directory in /data/web/wp-content/plugins/wordpress-social-login/hybridauth/Hybrid/Provider_Adapter.php on line 96
Fatal error: require_once(): Failed opening required '/data/web/wp-content/plugins/wordpress-social-login/hybridauth/Hybrid/Providers/500px.php' (include_path='.:/php/includes:/data/KeywordServer/') in /data/web/wp-content/plugins/wordpress-social-login/hybridauth/Hybrid/Provider_Adapter.php on line 96
The path used is incorrect.
Note that the file requested is "500px.php", while the file on disk is "px500.php".
This can be fixed by renaming the px500.php file to 500px.php, and changing the name of the class defined in that file to match.