WordPress Critical Error After a PHP Update: How to Fix It

Key takeaways

• The error is common and fixable. WordPress.org's common errors page says this message means something on the site caused a critical error. It lists plugin conflicts, theme problems, an incompatible PHP version, a reached memory limit and corrupted files as the usual causes (checked 22 October 2026).
• First, get the site back. Switch PHP to the version that worked before, then work on the cause with the site live again. Keep that rollback brief. The October 2026 PHP security advisory offers no official patch for PHP 8.1 or anything older.
• Check the admin email. The message itself tells you to look in your site admin inbox for instructions. Start there before you touch anything.
• The log names the culprit. Turning on debug logging writes the error to wp-content/debug.log, and that file usually points to one plugin or theme.
• Deactivate by renaming a folder. WordPress.org gives this as the way in when you are locked out of the dashboard. It keeps your plugin settings.
• Know when to stop. If the log points at your theme's core code, the database, or you cannot reach your files, ask for help. A calm hand-over beats a guess on a live site.

What the message means, and why a PHP change causes it

When a plugin or theme was written for an older PHP, a newer PHP can refuse to run its code. The page stops and WordPress shows the critical error notice or a blank white page. WordPress.org calls the blank page the White Screen of Death and gives plugin and theme problems as its two main causes.

WordPress core can run on old PHP while an old plugin may not run on a new one, as the WordPress minimum PHP version article explains. The answer is to find the one piece of code that does not fit, not to stop updating.

Match your symptom to a likely cause

The table below uses only the causes WordPress.org's pages support. It is a guide to where to look first, not a diagnosis.

PHP version is one possible cause, not the only one, so the log matters.

The fix, in order

Work down the list and stop as soon as the site is back.

1. Take a copy of what you have. If you can reach your files or have a recent backup, make sure one exists before you change anything. WordPress.org's troubleshooting FAQ reminds site owners to back up both files and database before upgrades.
2. Open the admin email. Look in the inbox of the administrator address for the message WordPress sent. The notice on screen tells you to check it for instructions.
3. Switch PHP back at your host. Pick the version that was running when the site last worked. The setting's location is shown in our PHP version check and update guide. Your host's support can do it if you cannot find it. Do this to get visitors back, not as the place to stay.
4. Turn on the error log. Add the lines below to wp-config.php, above the line that tells you to stop editing. Source: the WordPress developer debugging page, checked 22 October 2026.
5. Reload the broken page, then read the log. Open wp-content/debug.log. Look for the word Fatal and the file path next to it. A path with /plugins/ in it names a plugin. A path with /themes/ names a theme.
6. Deactivate the culprit by renaming its folder. Use FTP or your host's file manager. Go to wp-content/plugins and rename the one plugin's folder, for example by adding -off to its name. For the theme, rename the active theme's folder in wp-content/themes, and WordPress falls back to another installed theme.
7. Update or replace it. Install a newer version of that plugin or theme, or find a maintained alternative. Rename the folder back only when the new version is in place.
8. Switch PHP forward again and test. Move to the fixed release you are aiming for, then test the home page, a form, login and the admin area.
9. Turn the logging off. WordPress.org says debug tools are not recommended on live sites, so remove those lines when you are done.

Add these three lines:

`` define( 'WP_DEBUG', true ); define( 'WP_DEBUG_LOG', true ); define( 'WP_DEBUG_DISPLAY', false ); ``

Logging with WP_DEBUG_LOG needs WP_DEBUG switched on, and the file lands in wp-content/debug.log unless you change it. WP_DEBUG_DISPLAY set to false stops errors from showing in front of your visitors.

If you cannot tell which plugin it is

Sometimes the log is long, or the error is not clear. WordPress.org's own method is to deactivate everything and bring plugins back one at a time.

WordPress.org's FAQ describes this and notes you must reactivate each plugin by hand. It also describes a database route through phpMyAdmin, and tells anyone unfamiliar with it to ask their host or a developer.

If the site still fails with every plugin off, the theme is the next suspect. WordPress.org suggests switching to a default theme, and renaming the active theme's folder if you are locked out.

When to stop and call someone

Stop and get help if any of these are true:

• You cannot reach your files. If you have no FTP, no file manager and no host login, you cannot do the steps above safely.
• The log points at WordPress core or at a file you do not recognise. WordPress.org lists corrupted WordPress files as a cause, and the repair is a restore or a fresh copy of core, which needs care.
• The site takes orders or bookings. Every hour down costs money. See our note on WooCommerce and the PHP flaw.
• You rolled back to PHP 8.1 or older and cannot move forward. That version has no official fix, so the clock is running.
• You suspect the site was hacked, not just broken. Our guide to checking whether a WordPress site is hacked lists the signs. A broken site and a hacked site can look alike.

If you decide to hand it over, our note on what to check when hiring someone to update PHP can help you ask the right questions. Share an administrator invite, and never send a password in chat.

Limits of this guide, and cases it does not cover

• Your exact cause is beyond what we can name from here. WordPress.org lists five usual causes. Which one is yours depends on your log, your plugins and your host.
• The email details are not in the pages we read. WordPress.org's common errors page says the notice points you to the admin email. It does not describe the contents or any recovery link, so we have left that part out. If your email includes a link, follow what that email says and treat it as the host's or WordPress's own message only if it came to your admin address.
• This is not for a hosted builder. Webflow, Shopify, Wix, Squarespace and Framer do not give you a PHP setting to roll back. The question is covered in whether Webflow runs PHP.
• Rolling back keeps you exposed. The fix for the October flaw is the newer PHP. Stay on the older version just until you locate the broken code. If you are unsure what state your server is in, read the questions to ask your host about the PHP fix.

How we help at Amariq

If your site is down right now, the first job is to get it back, and the cause can wait. Our team handles PHP changes on WordPress sites and had finished a number of them by the day after the advisory, so a critical error screen is a familiar sight to us. We can roll PHP back, find the plugin or theme at fault, fix or replace it and then try the newer version again. Ask for that through the WordPress PHP update gig on Fiverr, which is the quickest route. Our WordPress development page lists the wider services. Client reviews on Fiverr and Upwork are public, and our YouTube channel shows how we work.

Frequently asked questions

What does "There has been a critical error on this website" mean?

WordPress.org says it means something on the site caused a critical error. The usual causes it lists are plugin conflicts, theme compatibility issues, an incompatible PHP version, reaching the memory limit and corrupted WordPress files. The message also tells you to check your admin email inbox for instructions.

Why did my site break right after a PHP update?

Most often, a plugin or theme was written for an older PHP and does not run on the newer one. The error log shows which file failed. Updating that plugin or theme, or replacing it, is usually the cure.

Can I just go back to the old PHP version?

It gets your site back, but it is not a long term answer. No official fix exists for PHP 8.1 and older against the October 2026 flaws. Keep the rollback only while you find the broken code, then move forward again. Our PHP end of life dates guide shows where each version stands.

I cannot log in to the dashboard. How do I deactivate plugins?

Use FTP or your host's file manager. Rename the plugins folder inside wp-content, for example to plugins.hold, and WordPress treats every plugin as off. Log in, rename the folder back, and reactivate plugins one by one. WordPress.org describes this method on its troubleshooting FAQ.

Where do I find the error log?

Turn on WP_DEBUG and WP_DEBUG_LOG in wp-config.php. WordPress then writes errors to wp-content/debug.log by default. Switch the lines off again when you finish, because WordPress.org does not recommend debug tools on live sites.

Could memory be the problem instead?

Yes, it is on WordPress.org's list of causes. If the error says allowed memory size is exhausted, the page's fix is to raise the limit in wp-config.php, or in php.ini if you are comfortable editing it. On shared hosting you may need to ask your host to raise it.

How much will it cost to have someone fix it?

It varies by site. Our quotes come from the scope of the work, never an hourly rate. The fastest way to a real answer is to share what the error says and what changed. For a regular fix with the update done properly, our website maintenance cost guide shows how care plans compare.