Today, I installed a new plugin to display Related Posts within the content of each blog posts, Previously I was using Jetpack’s Related post module.

Jetpack was also giving *Your website needs to be publicly accessible to use Jetpack site_inaccessible error. I have also written about this issue.

After installing the new plugin for Inline related Posts, I decided to deactivate Jetpack’s Related Post Module.

I saw following error:

Error updating Related Posts settings. Error: Cookie nonce is invalid.

After reading some threads on WordPress.org, I found out a very simple solution.

Solution 1: Error: Change WP Super Cache Settings

I am using WP Super Cache plugin to improve site speed and this plugin was causing the error. Thanks to Cornel Manu for sharing this solution at WordPress forums.

Cornel was able to use JetPack after deleting the WP Super Cache plugin.

OMG guys. I found the error. I deleted the WP Super Cache plugin because I want to use another one. Now it worked to activate the WordPress function. It has something to do with WP Super Cache htaccess rules.

Disabling it didn’t work for @kemikalelite probably because the htaccess rules were still there. @kingmanu

If you are using WP Super Cache plugin, log in to your WordPress Dashboard, Go to Settings > WP Super Cache and under advanced settings, deactivate following setting.

Make known users anonymous so they’re served supercached static files.

You can see the screenshot below.

If above method does not work try to uninstall the caching plugin and delete rules from htaccess file.

Jetpack started working again immediately after deleting the rules from htaccess and disabling the cache plugin. @kemikalelite

Solution 2: Disable SuperSonic plugin

Mr Cezariusz Marek posted at WordPress forums that he was able to activate Jetpack plugins after disabling the SuperSonic plugin: https://wordpress.org/plugins/supersonic/

Other possible solutions

If you are using any caching plugin (W3 Total Cache etc) for WordPress, try to disable the caching plugin. If it does not work then delete caching plugin and try to use JetPack.

I found these solutions at WordPress forums. You can read the thread [Jetpack 4.3] Error: Cookie nonce is invalid at WordPress forums.