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Fixing the 'call_user_func_array(): Argument #1 ($callback) must be a valid callback' Error in WordPress

29 threads Sep 7, 2025 Core → Localhost installs

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If you're developing a WordPress site locally, you might encounter a confusing and site-breaking error: Fatal error: Uncaught TypeError: call_user_func_array(): Argument #1 ($callback) must be a valid callback. This error frequently appears in the class-wp-hook.php file and can prevent you from accessing your dashboard or viewing your site. Let's break down what this error means and the most effective ways to resolve it.

What Does This Error Mean?

At its core, this error is a PHP TypeError. WordPress uses a system called hooks (actions and filters) to allow themes and plugins to modify its behavior. The call_user_func_array() function is used to execute these hooked functions. The error occurs when WordPress is told to run a specific function (the "callback"), but that function either doesn't exist, is misspelled, or is being called incorrectly (e.g., a non-static method called statically).

Common Causes

Based on community reports, this error is almost always caused by code in a theme or plugin. Common specific triggers include:

  • A theme or plugin trying to call a function that has been removed or renamed.
  • A misspelled function name in a theme's functions.php file.
  • A function that is defined in the wrong scope (e.g., a non-static method being hooked statically).
  • A incompatibility between a theme and a specific plugin, or vice versa.
  • Corrupted or incomplete theme/plugin files, often from a failed update or manual edit.

How to Troubleshoot and Fix the Error

Since this error often locks you out of the WordPress admin dashboard, you will need to use alternative methods to access your site's files, such as FTP, SFTP, or your localhost's file manager (e.g., navigating through XAMPP's htdocs folder).

Solution 1: Switch to a Default Theme (Most Common Fix)

The most frequent culprit is the active theme. If you recently activated a new theme and the error appeared, the theme's code is likely the source.

  1. Via your file manager, navigate to /wp-content/themes/.
  2. Find the folder for your currently active theme.
  3. Rename the theme's folder (e.g., from my-theme to my-theme-old).
  4. This will force WordPress to deactivate the faulty theme and fall back to a default theme like Twenty Twenty-Four.
  5. Reload your site. If the error disappears, you have confirmed the theme was the problem. You will need to contact the theme's developer for support or find an alternative.

Solution 2: Deactivate All Plugins

If the error persists after switching themes, a plugin is likely causing the conflict.

  1. Via your file manager, navigate to /wp-content/plugins/.
  2. Rename the plugins folder to plugins.old.
  3. This will deactivate every plugin simultaneously.
  4. Reload your site. If the error is gone, a plugin was the cause.
  5. Rename the folder back to plugins.
  6. Rename individual plugin folders one by one, reloading your site after each, until you identify which plugin causes the error. Once found, keep that plugin deactivated and seek support from its developer.

Solution 3: Enable Debugging for More Information

If the above steps don't isolate the issue, enabling WordPress debugging can provide a more specific error message that points to the exact file and line of code causing the problem.

  1. Open your wp-config.php file (located in your WordPress root directory).
  2. Find the line that says define('WP_DEBUG', false);.
  3. Replace it with the following lines: 
    define('WP_DEBUG', true);
define('WP_DEBUG_LOG', true);
define('WP_DEBUG_DISPLAY', false);
  4. Save the file and reload the page where the error occurs. This will write detailed errors to a log file (/wp-content/debug.log) instead of displaying them on screen. Check this log for more precise clues.

Conclusion

The call_user_func_array() error can be alarming, but it is almost always resolvable by systematically identifying a conflicting theme or plugin. The recommended first step is to switch to a default WordPress theme by renaming your active theme's folder. If you continue to have problems, the community at BugWP.com is a great resource for further help.

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