Call to undefined function add_settings_error()

are you talking about the following plugin?

https://tr.www.ads-software.com/plugins/postie/

Yes. That’s the one.

Hello,
I have same problem, but I do not know which plugin…

When I try login to dashboard, then I get fatal error 500 and these logs:

[17-Nov-2018 15:10:58 UTC] PHP Fatal error:  Uncaught Error: Call to undefined function add_settings_error() in site/public_html/wp-content/plugins/wp-fastest-cache/wpFastestCache.php:286
Stack trace:
#0 site/public_html/wp-content/plugins/wp-fastest-cache/wpFastestCache.php(1063): WpFastestCache->notify(Array)
#1 site/public_html/wp-content/plugins/wp-fastest-cache/wpFastestCache.php(771): WpFastestCache->deleteCache()
#2 site/public_html/wp-includes/class-wp-hook.php(286): WpFastestCache->on_all_status_transitions('publish', 'new', Object(WP_Post))
#3 site/public_html/wp-includes/class-wp-hook.php(310): WP_Hook->apply_filters(NULL, Array)
#4 site/public_html/wp-includes/plugin.php(453): WP_Hook->do_action(Array)
#5 site/public_html/wp-includes/post.php(4128): do_action('transition_post...', 'publish', 'new', Object(WP_Post))
#6 site/public_html/wp-includes/post.php(3588): wp_transition_post_status('publish', 'new', Object(WP_Post))
#7 site/public_html/wp-content/ in site/public_html/wp-content/plugins/wp-fastest-cache/wpFastestCache.php on line 286

I fixed the problem. Please delete wp fastest cache and download again to get the latest changes because I did not release a new version.

Thanks Emre. That did the trick.

you are welcome ?? if you vote, you make me so happy.

https://www.ads-software.com/support/plugin/wp-fastest-cache/reviews/?rate=5#new-post

Had the same problem – seems to be VERY common. The fix suggested worked.