在页面上显示下面的错误：

Fatal error: Class ‘WP_Metadata_Lazyloader’ not found in /home/minhtamblog.com/public_html/wp-includes/meta.php on line 865

我是完全按着升级指导做的，bing和baidu都没找到有用的信息，后来google到结果，因为4.5的wp-settings.php也做了改动，所以要把4.5中这个文件copy到你的目录里！然后问题解决了！

原文的回答貌似是“替换全部文件”（ If you did only a partial installation, and did not update ALL the files, including those in the root directory, like wp-settings.php, then yeah, your site will remain broken. MANUALLY UPDATE ALL THE FILES. That will fix this problem. ）

原文地址：https://wordpress.org/support/topic/wordpress-45-error-after-update