I was trying to upgrade WordPress to latest version 4.7.1 from the dashboard following these steps to upgrade WordPress automatically. After I hit the Update Now button from Dashboard >> Updates, I was redirected to http://www.mysite.com/wp-admin/upgrade.php?_wp_http_referer=%2Fwp-admin%2F which is a blank page. I can’t access the admin area any more, the site is still up and working, just the dashboard can’t be accessed.
I found different ways to fix this issue on the web. Some suggest to match the database version in the version.php file and db_version field from the WP_Options table of the WordPress database, then edit the value in the options table to match the value in the php file. Tried this, not work. And also repaired WordPress database using phpMyAdmin, still no luck. All solutions I have found indicate there is something wrong with WordPress database. Sometimes when you manually update WordPress sites, you may need also update WordPress database. The problem now is how to bring up the WordPress database upgrade page see if any update required.
Finally I found a quick solution for this. You can simply rename the WordPress plugin folder, then visit the wp-admin page and get the Database Update Required screen and continue to finish updating WordPress. Note that there are various reasons WordPress dashboard is not working properly. By updating WordPress database, you can’t fix all WP admin panel not accessible problems. If you had the same problem with me, this solution should work for you as well.
There are different ways you can access the WordPress plugin folder and rename it. For example, you can connect to WordPress server through a FTP client and rename the folder. In you are using a cPanel web hosting, you can log on cPanel, go to File Manager, then browse to the WordPress site root folder, open wp-content sub-folder and find the plugins sub-folder. You can rename it to something like plugins-123, plugins-abc, or else. Then visit the admin URL, http://www.yoursite.com/wp-admin/, in your web browser and get above database update page and fix the issue. After the update of WP database, you may see some error. No worry. Go to change the plugins folder name back, the error should disappear instantly. Last but not least, go to WordPress Dashboard >> Plugins to enable plugins you need. By renaming the plugins folder, your active plugins may be disabled, thus we need to double check and make sure they are activated.