In this article I will show you have to fix WP ERROR: key not found!.
It is a strange error which I've encountered when I tried to reset the user password on one of my WordPress test websites.
But this does not mean that it cannot appear in other cases.
I checked a few things on my WordPress website and could not fix the error.
Then I realized thatI was using a custom page for the reset password feature. I was actually using a plugin called Frontend Reset Password Frontend Reset Password.
Then I was also using All In One WP Security. One of the settings, for this plugin, was to add "Enable Captcha on Lost Password Page".
When I disabled the "Enable Captcha on Lost Password Page" option, the error was fixed.
When you encounter this Wordpress ERROR: key not found!, you need to make sure that your Captcha or reCAPTCHA feature is working correctly. In my case it wasn't, so I had to disable that option.
Shortly, to fix "Wordpress ERROR: key not found!" you need to disable Captcha for reset password form (if the error appears after you submit reset password form).
If this appear appears after submitting different forms, you need to check Captcha or reCAPTCHA first.
I really hope that my tip will save some of your time, in case you will get this error on your WordPress website. This is one of the most weird errors in WordPress and I'm glad that I've found a simple solution and the actual cause of it.