I've managed to make the issue disappear! I've deleted from /home folder the .pulse folder. It seems that in that folder I had some "processes", or something like this, so quickly born and killed that I couldn't seen in the task manager and because of this the CPU was at 50% and maybe this was influencing also the polkitd service.
** Changed in: xserver-xorg-video-ati (Ubuntu) Status: Incomplete => Fix Committed -- The system is very slow. The memory is not freed after closing a program. (-pae) https://bugs.launchpad.net/bugs/569711 You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs