If you experience an error message like "Error: Class PDO does not exist" during installation of or update to LiveAgent version 4.0.43.8 or higher, then it is a reference to missing support of MySQL PDO in your webserver.
There are 2 possible solutions:
There are 2 possible solutions:
1) Have your hosting admin to install MySQL PDO extension to your webserver
2) Into accounts/settings.php file of Live Agent place:
DB_DRIVER=Mysql