This error shows up when you have compiled your PHP and Apache without MySQLi. It is an imporved and most secure version. You can install it by following below steps.
- Login to your WHM as root
- In left side bar, type ‘EasyApache’ in search box
- Click on EasyApache
- Select build option by scrolling down
- Once there hit “Start customizing based on profile”
- Here you can upgrade or degrade Apache version. Select desired version and click “Next Step”
- Now on this page you can do the same for PHP. Select version and click “Next Step”
- On this page check “Exhaustive Options List”
- Lookout for “MySQL Improved extension”
Save and build will start. It can take a long time depending on your server speed. Sit back and just wait. Once done, you will not get this error again.
If you are on shared server (which is not recommended at all) you need to ask your hosting provider to do that for you. Let us know if problem persists.