Title: Fatal Error upon initial activation
Last modified: February 13, 2020

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# Fatal Error upon initial activation

 *  Resolved [burkettd](https://wordpress.org/support/users/burkettd/)
 * (@burkettd)
 * [6 years, 4 months ago](https://wordpress.org/support/topic/fatal-error-upon-initial-activation/)
 * We’ve got WF paid and free on tons of sites all in the same environment. We’ve
   never gotten an fatal error after install.
 *     ```
       PHP Fatal error:  Uncaught Error: Call to undefined function filter_var() in /home/ninja_david/blowlow.com/wp-content/plugins/wordfence/waf/bootstrap.php:177
       Stack trace:
       #0 /home/ninja_david/blowlow.com/wp-content/plugins/wordfence/waf/bootstrap.php(150): wfWAFWordPressRequest->_isValidIP('68.61.138.138')
       #1 /home/ninja_david/blowlow.com/wp-content/plugins/wordfence/waf/bootstrap.php(70): wfWAFWordPressRequest->_getCleanIPAndServerVar(Array)
       #2 /home/ninja_david/blowlow.com/wp-content/plugins/wordfence/vendor/wordfence/wf-waf/src/lib/waf.php(259): wfWAFWordPressRequest->getIP()
       #3 /home/ninja_david/blowlow.com/wp-content/plugins/wordfence/waf/bootstrap.php(814): wfWAF->run()
       #4 /home/ninja_david/blowlow.com/wp-content/plugins/wordfence/wordfence.php(69): require_once('/home/ninja_dav...')
       #5 /home/ninja_david/blowlow.com/wp-admin/includes/plugin.php(2223): include('/home/ninja_dav...')
       #6 /home/ninja_david/blowlow.com/wp-admin/plugins.php(175): plugin_sandbox_scrape('wordfence/wordf...')
       #7 {main}
         thrown in /home/ninja_david/blowlow.com/wp-content/plugins/wordfence/waf/bootstrap.php on line 177
       ```
   

Viewing 5 replies - 1 through 5 (of 5 total)

 *  [WFGerroald](https://wordpress.org/support/users/wfgerald/)
 * (@wfgerald)
 * [6 years, 4 months ago](https://wordpress.org/support/topic/fatal-error-upon-initial-activation/#post-12428760)
 * Hey [@burkettd](https://wordpress.org/support/users/burkettd/),
 * Can you please try reinstalling a fresh copy of Wordfence with all other plugins
   disabled and let me know if you still receive the error?
 * Please let me know.
 * Thanks,
 * Gerroald
 *  Thread Starter [burkettd](https://wordpress.org/support/users/burkettd/)
 * (@burkettd)
 * [6 years, 4 months ago](https://wordpress.org/support/topic/fatal-error-upon-initial-activation/#post-12429200)
 * Thank you for the quick response [@wfgerald](https://wordpress.org/support/users/wfgerald/),
 * I tried it and ran into the same issue. The support team at our host pinned it
   down to a PHP compatibility issue. The site was set up on PHP 7.4. They rolled
   it back to 7.3 and the problem was solved.
 *  [WFGerroald](https://wordpress.org/support/users/wfgerald/)
 * (@wfgerald)
 * [6 years, 4 months ago](https://wordpress.org/support/topic/fatal-error-upon-initial-activation/#post-12429253)
 * Hey [@burkettd](https://wordpress.org/support/users/burkettd/),
 * Thanks for sharing this. I’ll definitely do some testing.
 * Please let us know if anything else comes up.
 * Thanks,
 * Gerroald
 *  Thread Starter [burkettd](https://wordpress.org/support/users/burkettd/)
 * (@burkettd)
 * [6 years, 4 months ago](https://wordpress.org/support/topic/fatal-error-upon-initial-activation/#post-12429315)
 * Thanks [@wfgerald](https://wordpress.org/support/users/wfgerald/), let me know
   if you would like any more information.
 * [@moderator](https://wordpress.org/support/users/moderator/) – is there any way
   we can remove part of the topic text above that shows the folder structure and
   username? That was my fault for not removing it for security reasons.
 *  Moderator [Jan Dembowski](https://wordpress.org/support/users/jdembowski/)
 * (@jdembowski)
 * Forum Moderator and Brute Squad
 * [6 years, 4 months ago](https://wordpress.org/support/topic/fatal-error-upon-initial-activation/#post-12431861)
 * _*Looks*_
 * I am sorry, but no. There is no security issue here.
 * [https://wordpress.org/support/forum-user-guide/faq/#will-you-delete-my-post-or-my-link-within-my-post](https://wordpress.org/support/forum-user-guide/faq/#will-you-delete-my-post-or-my-link-within-my-post)
 * Search engine hits are _never_ considered extreme. The post will not be edited
   or deleted.
 * Also you’re a customer and cannot get Wordfence support here.
 * For pro or commercial product support please contact the author directly on their
   site. This includes any pre-sales topics as well.
 * As the author is aware, commercial products are [not supported in these forums](https://wordpress.org/support/guidelines/#do-not-post-about-commercial-products).
   I am sure they will have no problem supporting you there.

Viewing 5 replies - 1 through 5 (of 5 total)

The topic ‘Fatal Error upon initial activation’ is closed to new replies.

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 * 5 replies
 * 2 participants
 * Last reply from: [Jan Dembowski](https://wordpress.org/support/users/jdembowski/)
 * Last activity: [6 years, 4 months ago](https://wordpress.org/support/topic/fatal-error-upon-initial-activation/#post-12431861)
 * Status: resolved