This warning has appeared at the top of our website, and our top menu bar has disappeared:

Warning: call_user_func_array) expects parameter! +~ be a valid callback, function 'smartwp_remove_wp_block_library_css' not found or invalid function name in /home/customer/www/stpetersmedford.org/public_r includes/class-wp-hook.php on line 307

I don’t know how to decipher this message nor how to fix the problem. Are the two things related (disappearance of top menu, this warning)?

Thank you for any help.

  • It looks like at some point you followed this: smartwp.com/remove-gutenberg-css But didn't properly delete all the code. Or you renamed the function without renaming the action callback. Commented Apr 8, 2022 at 4:45

1 Answer 1


This function, call_user_func_array() is called by add_filter() (or add_action()) that was not declared properly. Scan the code for something like:

add_filter('something', 'smartwp_remove_wp_block_library_css')

to find the culprit. If you do find it and it wasn't something you added/changed, you will have to troubleshoot to determine why this function was not declared/found.

The top menu is still there - you can see it very faintly at the very top of the page as you mouse over the area just above the warning message.

One last thing - it looks like you have display_errors enabled, which is not good practice for a public facing website.

  • How do I disable display_errors?
    – user221064
    Commented Apr 14, 2022 at 18:09
  • display_errors could be enabled in wp-config.php, or in .htaccess, or in php.ini (you need to determine which one is loaded in your configuration), or even in httpd.conf. Start with wp-config.php to see if that's where it is enabled - reference https://wordpress.org/support/article/debugging-in-wordpress/.
    – ScottM
    Commented Apr 15, 2022 at 0:07

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