What about dhcpcd? or any terminal commands? I would try things like for example #iwlist wlan0 scan , #dhcpcd eth0 , check the man file if you have wicd, I'm "fairly" sure you can command line that with ncurses installed. Check the man NetworkManager file as well. Along with the file the error is coming from, although I'v no idea how much you know of network setup. Assuming not much, do a #ifconfig , then if your device is listed its at least up, if not, #ifconfig -a , if this brings up anything new IE: wlan0, usb0, eth0 ... use the #ifconfig up command to turn it on. These are pretty basic things so I dont know how much it would help you. I do know that when all else fails manually setup your net. files (a bit complicated for your error so i doubt thats it.) also you could reconfigure NetworkManager. Oh and possibly remove the file if all else fails, reboot and see if you can auto connect? recompile networkmanager.. sometimes those small errors are easily worked around and sometimes not so I'm just thinking of some abstract possibilities for you, and just reinstall networkmanager with the file deleted, just use --oneshot with emerge i would think you'd be fine with that. Oh and don't change anything you don't understand, or cp <file/path/to/file.whatever> to <file/path/to/file.whatever.OLD> so if something goes wrong you still have it. Gentoo documentation would also possibly help for manually configuring anything. Some thoughts.. but I'm also pretty careless so I would not advise listening to me much, as i would just edit the file, or some of the above until it worked.
#EDIT: looked into quickly and a common fix seems worth trying these:
#this in your default-polkit-privs.local ( this would be your /etc/default whatever privs.local file here)
#then, and im assuming your file names may be different than this so you might want to check.
#this would, i assume work. if not, try something like this:
#make a polkit.mods in your $HOME (if u dont have one) and add these into a file with vi/vim
#save it in there and do a :
su -C 'cat polkit.mods >> /etc/polkit-default-privs.local ; set_polkit_default_privs'
#^^^ thats what i found, you will most likely have to modify file locations / names to suit because that shits not even close on my non synced system atm and im sitting here moding files =/ needed a break hope it helps.