by Phuong Hoang.
Hi Helen and Damyon,
Certainly, I uninstalled auth_googleoauth2 before upgrading.
Basically I resolved my error. It was my fault; I modified block_login.php in the previous version, then I reused this file in the new one - deleted the old file and uploaded the new one - resolved my error. However, Oauth 2 services only works normally when I untick "Prevent account creation when authenticating". ButI get errors“The login attempt failed. Reason: An account with your email address could not be found.” when I tick "Prevent account creation when authenticating". But I prefer "Prevent account creation when authenticating". In addition, the emails that having logged in the site via auth_googleoauth2 may cause problems so we have to delete them. Unfortunately, I have hundreds of them.Thanks for your reply and your time,