Fatal error undefined function is_network_admin()

Problem Description:

When you upgrade WordPress, a fatal error undefined function is displayed when you try to log in_network_Admin() fatal error.

Solution: upgrade manually

This error is caused by the WordPress upgrade failure. Try upgrading manually.

1. Download the latest WordPress package and unzip it.

2. Back up your current WordPress.

3. Rename the WP includes and WP admin directories to WP includes.bak and wp-admin.bak.

4. Upload WP includes and WP admin directories to the server via FTP.

5. Upload the contents of the new WP content directory to the corresponding location on the server.

6. Upload other files to the WordPress root directory.

7. Delete the. Maintenance file through FTP.

8. Log in to WordPress again and you will see a link like http://your domain name/WordPress/WP admin/upgrade.php. Follow the instructions.

9. Empty the cache and see if you have taken effect.