If you are running an old version of WordPress, chances are you might encounter a problem updating to the newest version or when trying to update plugins.
I got this message when trying to update an old site:
"SSL certificate problem: unable to get local issuer certificate"
As far as I can understand from this helpful post the reason is that the WordPress team included a CA certificate check from version 3.7.0 - so this will cause WordPress to complain since you are not verifying the connection in your current version.
Add these lines of code to the very end (otherwise will break your site) of your wp-config.php file located in your root directory:
add_filter('https_ssl_verify', '__return_false'); add_filter('https_local_ssl_verify', '__return_false');
Here is an example of how it should look like:
After updating, you should be able to remove these lines of code.
Edit: This might be a very common Xammp error. I have read several posts about issues with certificates in Xammp and my problem was also only occuring on my localhost where i run Xammp. Here is a related problem and a general fix