I was dancing about exactly same problem last 4 days. Now it looks I finally solved it.
In my case was problem the php extension "Suhosin".
So I disable it by custom php.ini in administrator folder. But after that disappeared main administrator menu. So I find, there is some bug in php or apache, when you are using custom php.ini, and this bug disable PDO extension as well. So I have to enable PDO again in my php.ini.

My php.ini in admin folder is like this:

extension=pdo.so
extension=pdo_sqlite.so
extension=sqlite.so
extension=pdo_mysql.so
suhosin.simulation = On


Check if is on your server used bloody "Suhosin".