PDO is a PHP extension - sure, that this is installed and usable? Tried a server restart (I´d to do this, for example).
May your DB-port is a non-standard-port? You´re able to configure your connection settings around line 217 in "protected/config/main.php ".
Also you may want to check your "php.ini" for the path to the PDO/PHP extentions (they might be changed to a PHP upgrade).
- X2Peter likes this