Howdy Camate. I ran into this error recently myself. I was zoning a character from North Sandy into Port Sandy - Port never loaded, the character dc'd and couldn't get back in with the FFXI-3001 error. I logged in to a second character on the same POL ID in a different zone and it worked just fine. No rebooting or powering off of anything. I tried to log in to a third character on the same POL ID which I knew I had left in Port Sandy and that one wasn't able to log in and got the same FFXI-3001 error.
This happened on a weekend and I called a GM and they told me to wait until Monday and call support. The problem cleared itself after an hour or two without me doing any of the things listed in the knowledge base article. I don't see how any of the things in the knowledge base article would make a difference if I'm able to log in to some characters but not others, based on what zone they happened to be in when I logged them out. My firewall/router won't be blocking a specific ffxi character. :P To me it sounded like a problem with that specific zone.