i had the EXACT same error before... i kinda have an idea on how to fix it - sorry for the HUGE post
ok... i have a couple of solutions...
solution#1: run the network wizard again on both of your computers... don't forget to CROSS YOUR FINGERS (ok, this solution sucks)
solution #2: make sure that both of your computers are on the same network... (not the network name)... let me explain:
i am assuming you have more than one computer... well, IF they have two different external IP's, make sure that the two ip's are on the same network (figure out the network and the host bits by using the subnet mask... yea, go grab a piece of paper and a pen) ... for example, back when i used 2 external ip's, sometimes one came in the 142.x.x.x range, while the other one came up in the 64.x.x.x range... (OBVIOUSLY NOT the same network) that's when i ran into problems... in fact, the two computers couldn't even ping each other AT ALL... (obviously filesharing was a no-go) ---- if its possible for your computers to get two differnet ips go to solution#3
solution#3: use a router to get only one external IP... if you don't feel like buying or setting one up, go to solution#4
solution#4: ICS (Internet Connection Sharing)
Make sure you have TWO ethernet connections in one computer, and use ICS (start it through the network wizard). ICS will allow you to get only ONE external IP (one ethernet card) and you'll have an internal network (192.168.0.x) on the other ethernet card... basically your "primary" computer will be a a DHCP server and assign an internal ip to the other computer (use a crossover cable for a direct connection, or a hub/switch)... [disadvantage] when you turn off your primary computer you'll lose the internet on all connected through it [/disadvantage] but i think its well worth it {i have had this setup for about 2 months now, and i have never had a problem - i also had a 10 base hub before... and now my connection between computers is 100 base}
you're a smart guy... you can figure out ICS... one pointer: in your network connection property click "share this connection" on the one that's connected to the internet, and NOT the other one <-- had me wondering for a while
********** final comments ************
even if your computers don't get 2 external ip's its still better (IMO) to have an internal network so go to sol'n #3 or #4
i really hope this helps you (cuz it took a long time to write)... but i don't know whether you want to redesign your whole network... although give #3 or #4 a shot
best of luck,
-Fil