authentication is required to set the network proxy used for downloading packages. An
application is attempting to perform an action that requires privileges.
Authentication as the super user is required to perform this action" and asking
for the root password.
I didn't have the root password for this machine and hitting cancel would just bring back the pop-up in a few minutes. After googling here is the best way i found to fix this problem:
From a terminal window run "gnome-session-properties" and un-check "PackageKit
Finally restart your vncserver and the issue should be gone.