Look in /home/<your-username>/.config/autostart for the file polkit-gnome-authentication-agent-1.desktop. Delete this file! The gnome-policy-kit will not try to start up on login after.
This file exists in /usr/share/lxde/polkit : and it is recreated in the home of the user at each new session : I did a series of tests in Virtualbox last night, and this morning, after turzin told me about the error message yesterday and asked me to test his last version with an update just after install. (He wanted to be sure he didn't mess something while tweaking things). Among other tests I tried to remove this file, reloaded the session, it was here again.
I suggested the simple solution here, deduced from the page at redhat bugzilla, as Texstar and Neal have already seen:
The new lxpolkit package generates an error at login in Lxde (Solution found). If you just leave the lxpolkit.conf do it's job and add the line:
NotShownIn=LXDE;right at the end of the file /usr/share/lxde/polkit/polkit-gnome-authentication-agent-1.desktop, /home/user/.config/autostart/polkit-gnome-authentication-agent-1.desktop, same under /root, and in /etc/skel, it should solve it for all : the problem has been solved in my Lxde in Vbox. (Rebooted twice since, and the message didn't appear again).
Doesn't matter now as I will remove it from the lxde-common package.
That's the info I was looking for, Thanks !
Happy End of Year !

Mélodie
PS: I wonder if you could rather setup lxpolkit to be a dependency of lxde-common rather than being a dependency of pcmanfm ? How will the system react if someone wants to use pcmanfm in another desktop than Openbox or Lxde ?