Hey, I’ve run into this exact error a bunch of times—let’s break down why it’s happening and how to fix it quickly. The error means your WordPress site can’t find the wp() function, which lives in wp-includes/functions.php. This almost always happens because the wp-load.php file (which loads all core WordPress functions) isn’t being loaded correctly from wp-blog-header.php.

Here’s what you can do step by step:

1. Check if wp-load.php exists in your root directory #

First, log into your server via FTP or your hosting control panel and head to your public_html folder. Verify that wp-load.php is present. If it’s missing:

• Download the exact same version of WordPress you’re using from the official site.
• Extract the zip file, grab the wp-load.php file, and upload it to your site’s root directory.

2. Fix the wp-load.php path in wp-blog-header.php #

The line require_once( dirname(__FILE__) . '/wp-load.php' ); relies on relative paths, which can break if your file structure changed (e.g., moving to a subdirectory, or PHP version differences). Try replacing it with an absolute path instead:

require_once( '/home/your-username/public_html/wp-load.php' );

Make sure to replace /home/your-username/public_html/ with your actual server path to the root folder.

3. Verify file permissions #

Incorrect permissions can prevent PHP from reading core files. Set these permissions using FTP or your hosting panel:

• For wp-load.php and other core files: 644
• For directories like wp-includes and wp-admin: 755
  Avoid setting permissions to 777—it’s a huge security risk.

4. Replace damaged core files #

If wp-load.php or other core files are corrupted:

• Download the matching WordPress version zip.
• Extract it, then delete the wp-content folder from the extracted files (we don’t want to overwrite your themes/plugins).
• Upload the remaining wp-admin, wp-includes folders, and all root files (except wp-config.php) to your server, overwriting the existing ones.

5. Rule out plugin/theme conflicts #

Sometimes a bad plugin or theme can interfere with core file loading:

• Rename your wp-content/plugins folder to plugins_old—this disables all plugins. If the site loads, rename folders one by one to find the culprit.
• Rename your active theme folder (in wp-content/themes) to something like theme_old, then WordPress will fall back to a default theme (e.g., Twenty Twenty-Four). If this fixes it, your theme was the issue.

Important Note #

Always back up your site (files and database) before making any changes—this way you can revert if something goes wrong.

内容的提问来源于stack exchange，提问作者naudi_alvarado