Critical error on my website due to WPML

This thread is resolved. Here is a description of the problem and solution.

Problem:
The client was experiencing a critical error on their website, which could not load at all. The error was triggered on wp-login.php with a message: 'Uncaught TypeError: in_array(): Argument #2 ($haystack) must be of type array, null given in /wp-content/plugins/sitepress-multilingual-cms/vendor/wpml/fp/core/Lst.php:203'. The client had questions regarding PHP 8.4.13 compatibility with WPML and the permanent fix for the error in Lst.php line 203.
Solution:
We recommended the following steps to resolve the issue:
1. Visit https://wpml.org/account/downloads/
2. Download fresh copies of all WPML plugins.
3. Delete the existing WPML plugins from the site (note: this will not remove translations or settings).
4. Upload the newly downloaded versions.
5. Try activating them again.
Additionally, we asked the client to confirm whether the installation was a standard WordPress setup or if there was a specific hosting environment or custom setup involved.

If this solution does not resolve your issue, or if it seems outdated or irrelevant to your case, we highly recommend checking related known issues at https://wpml.org/known-issues/, verifying the version of the permanent fix, and confirming that you have installed the latest versions of themes and plugins. If further assistance is needed, please open a new support ticket at WPML support forum.

This is the technical support forum for WPML - the multilingual WordPress plugin.

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Tagged: Exception

This topic contains 1 reply, has 0 voices.

Last updated by Andrey 4 months, 2 weeks ago.

Assisted by: Andrey.

Author	Posts
November 28, 2025 at 4:42 pm #17618739
cecileB-6	Background of the issue: I was trying to fix a critical error on my website, which could not load at all. I deactivated the WPML plugin by renaming it in the File manager, and the site came back to life. I attempted to update the plugin, but it was already up to date. The issue can be seen at: hidden link. Symptoms: The website experienced a critical error and could not load. A fatal error was triggered on wp-login.php: 'Uncaught TypeError: in_array(): Argument #2 ($haystack) must be of type array, null given in /wp-content/plugins/sitepress-multilingual-cms/vendor/wpml/fp/core/Lst.php:203'. The error occurred today, and the site broke completely. Recovery mode link expired. The plugin was temporarily disabled by renaming its folder. Questions: Can you confirm PHP 8.4.13 compatibility with WPML? What is the permanent fix for the error in Lst.php line 203?
November 28, 2025 at 11:39 pm #17619176
Andrey WPML Supporter since 06/2013 Languages: English (English ) Russian (Русский ) Timezone: Europe/Kyiv (GMT+03:00)	Thank you for contacting WPML support. Have you already tried the following steps? 1. Go to https://wpml.org/account/downloads/ 2. Download fresh copies of all WPML plugins. 3. Delete the existing WPML plugins from your site (this will not remove your translations or settings). 4. Upload the newly downloaded versions. 5. Try activating them again. Also, could you please confirm whether this is a standard WordPress installation, or if you are using a specific hosting environment or custom setup?