When I activate both plugins, login process through the side bar login plugin fails.
The response received is: Waring: Creating object from empty value (598).
Debugging that code you get that it's trying to set in WP_User (key = wp_native_dashboard_language) a value of "en_US". But the key doesn't exit at that point.
PHP versión is 5.4.7. I also checked that with a 5.4.4 PHP version it doesn't fail. I have read something about deactivating that execution warning echoed to the outpout.