Title: Fatal Error When Activating Collapsing Categories Plugin
Last modified: March 18, 2025

---

# Fatal Error When Activating Collapsing Categories Plugin

 *  Resolved [djwilko12](https://wordpress.org/support/users/djwilko12/)
 * (@djwilko12)
 * [1 year, 2 months ago](https://wordpress.org/support/topic/fatal-error-when-activating-collapsing-categories-plugin/)
 * Hi,
 * I’m experiencing a fatal error when trying to activate the _Collapsing Categories_
   plugin on my WordPress site. The error message I receive is:
 * `Fatal error: Uncaught TypeError: call_user_func_array(): Argument #1 ($callback)
   must be a valid callback, class CollapsCat does not have a method "init" in /
   wp-includes/class-wp-hook.php:324 Stack trace: #0 /wp-includes/class-wp-hook.
   php(348): WP_Hook->apply_filters('', Array) #1 /wp-includes/plugin.php(517): 
   WP_Hook->do_action(Array) #2 /wp-admin/plugins.php(196): do_action('activate_collap...')#
   3 {main} thrown in /wp-includes/class-wp-hook.php on line 324`
 * It seems like the plugin is trying to call an `init` method in the `CollapsCat`
   class, but that method doesn’t exist.
 * I have tried reinstalling the plugin, disabling other plugins, and checking for
   conflicts, but the issue persists. Could you please provide guidance on how to
   fix this?
 * Thanks in advance!
 * Best regards,

Viewing 4 replies - 1 through 4 (of 4 total)

 *  [Earl_D](https://wordpress.org/support/users/earl_d/)
 * (@earl_d)
 * [1 year, 2 months ago](https://wordpress.org/support/topic/fatal-error-when-activating-collapsing-categories-plugin/#post-18406505)
 * Experience the same thing.
 *  Plugin Author [robfelty](https://wordpress.org/support/users/robfelty/)
 * (@robfelty)
 * [1 year, 1 month ago](https://wordpress.org/support/topic/fatal-error-when-activating-collapsing-categories-plugin/#post-18443781)
 * I apologize for the issue. I just pushed a change to fix it in version 3.0.10.
 *  [jlreyest](https://wordpress.org/support/users/jlreyest/)
 * (@jlreyest)
 * [1 year ago](https://wordpress.org/support/topic/fatal-error-when-activating-collapsing-categories-plugin/#post-18473246)
 * Same problem here, and the last version published here is **3.0.9**.
 *  [papijo](https://wordpress.org/support/users/papijo/)
 * (@papijo)
 * [10 months ago](https://wordpress.org/support/topic/fatal-error-when-activating-collapsing-categories-plugin/#post-18595783)
 * Was experiencing the fatal error reported by the OP on version 3.0.9. No update
   available. Just deleted the plugin, downloaded again and activated it and … it
   works!
 * I expect Rob did the fix but forgot to change the version number from 3.0.9 to
   3.0.10?

Viewing 4 replies - 1 through 4 (of 4 total)

The topic ‘Fatal Error When Activating Collapsing Categories Plugin’ is closed to
new replies.

 * ![](https://ps.w.org/collapsing-categories/assets/icon-256x256.gif?rev=2886482)
 * [Collapsing Categories](https://wordpress.org/plugins/collapsing-categories/)
 * [Frequently Asked Questions](https://wordpress.org/plugins/collapsing-categories/#faq)
 * [Support Threads](https://wordpress.org/support/plugin/collapsing-categories/)
 * [Active Topics](https://wordpress.org/support/plugin/collapsing-categories/active/)
 * [Unresolved Topics](https://wordpress.org/support/plugin/collapsing-categories/unresolved/)
 * [Reviews](https://wordpress.org/support/plugin/collapsing-categories/reviews/)

 * 5 replies
 * 5 participants
 * Last reply from: [papijo](https://wordpress.org/support/users/papijo/)
 * Last activity: [10 months ago](https://wordpress.org/support/topic/fatal-error-when-activating-collapsing-categories-plugin/#post-18595783)
 * Status: resolved