Update Bug

What is your WordPress version before it updated?

Download and unzip a fresh copy of WordPress to your local drive:
http://ww.wp.xz.cn/latest.zip

FTP to your webspace. Delete the wp-admin and wp-includes folders. Delete the WordPress files in the root directory, except for the .htaccess and wp-config.php. Don’t touch your wp-content folder either.

Still in your FTP program, make sure you’re in Auto mode, then re-upload the wp-admin and wp-includes folders, and the files in the root directory, all from the fresh copy of WordPress you’ve just unzipped.