Title: Invalid function name error
Last modified: August 7, 2025

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# Invalid function name error

 *  [steph888](https://wordpress.org/support/users/stephcloete/)
 * (@stephcloete)
 * [9 months, 2 weeks ago](https://wordpress.org/support/topic/invalid-function-name-error/)
 * Hi everyone,
 * I hope someone might be able to help me. I’m reviving an old blog of mine and
   installed a new theme, etc. as well as a handful of plugins I’ve used on numerous
   other websites without issue. This site of mine though has given me one issue
   after the other that I had to fix. The last one has left me scratching my head.
   At the bottom of every page I get this error code:
 * call_user_func_array() expects parameter 1 to be a valid callback, function ‘
   wp_ob_end_flush_all’ not found or invalid function name in **/home/thenevzs/public_html/
   wp-includes/class-wp-hook.php** on line **324**
 * Though I’ve been working WordPress sites for a few years I’ve not learned as 
   much as I would hope. If someone could help me make sense of this issue and maybe
   tell me how to fix it I would be ever grateful. The website can be found here:_[
   redundant link deleted ]_
 * Thanks
 * Stephan
 * The page I need help with: _[[log in](https://login.wordpress.org/?redirect_to=https%3A%2F%2Fwordpress.org%2Fsupport%2Ftopic%2Finvalid-function-name-error%2F%3Foutput_format%3Dmd&locale=en_US)
   to see the link]_

Viewing 2 replies - 1 through 2 (of 2 total)

 *  Moderator [threadi](https://wordpress.org/support/users/threadi/)
 * (@threadi)
 * [9 months, 2 weeks ago](https://wordpress.org/support/topic/invalid-function-name-error/#post-18589428)
 * The function that is supposedly missing here has been part of WordPress Core 
   for a long time. It is strange if it cannot be found.
 * My recommendation would be to perform a manual update: [https://wordpress.org/documentation/article/updating-wordpress/#manual-update](https://wordpress.org/documentation/article/updating-wordpress/#manual-update)–
   this should bring the core files up to date. Alternatively, you can also click
   on Re-Install in the backend under Updates, which does the same thing.
 *  Thread Starter [steph888](https://wordpress.org/support/users/stephcloete/)
 * (@stephcloete)
 * [9 months, 2 weeks ago](https://wordpress.org/support/topic/invalid-function-name-error/#post-18589579)
 * Hi,
 * Thank you for the reply and I followed the manual update instructions. I went
   smoothly, but now there is a new error:
 * **Notice**: ob_end_flush(): failed to send buffer of zlib output compression (
   0) in **/home/thenevzs/public_html/wp-includes/functions.php** on line **5471**
 * Any ideas? I haven’t reactivated the plugins since doing the manual update, so
   I don’t think it’s one of them.

Viewing 2 replies - 1 through 2 (of 2 total)

The topic ‘Invalid function name error’ is closed to new replies.

## Tags

 * [call_user_func_array](https://wordpress.org/support/topic-tag/call_user_func_array/)

 * In: [Fixing WordPress](https://wordpress.org/support/forum/how-to-and-troubleshooting/)
 * 2 replies
 * 2 participants
 * Last reply from: [steph888](https://wordpress.org/support/users/stephcloete/)
 * Last activity: [9 months, 2 weeks ago](https://wordpress.org/support/topic/invalid-function-name-error/#post-18589579)
 * Status: not resolved

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