Step 1.
http://whatismyipaddress.com/ go to this website and check your IP adress, check it every 10 minutes, if it stays the same for 30 minutes you do not have IP changing issues.
Step 2. Log into your usenet account, I assume you use giganews.com, log in and change your password, then go to your server setup and also edit the new password in there.
Now everything should be fine. The error you are getting basically says: You can only connect from ONE internet connection at the same time and you are ALREADY CONNECTED through another internet connection. Now this other internet connection could be your OLD IP adress which keeps switching due to instability which you can test with my Step 1. OR someone else is using your account and you should change the password as in Step 2.
ps. If you're not home for example and the computer in your home is already connected this is what happens! So either dont connect from 2 places at the same time, OR get a newsserver that actually allows it. For now however find out why its reporting you're already connected, good luck.