Hallo,
i´m from germany and got the same problem, but here is my solution. First i will say, i had tested all, 3 kinds of routers, without firewall and defender, exposted host etc. Nothing had changed this problem. Then I had installed LFSs on my working PC with XP home, connected with the same router (Fritzbox 7270) and its running fine!! I can connect to all Servers in Router-Mode. Trying two minutes later with my gaming PC on Vista 64bit, i bacame the error message.
then i got it!! I have an onboard lan card on an asus board. A few minutes ago i had installed a second lancard from logilink, now its running without an error.
Don´t know why, but ists running
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I´m very happy now.
Hope i will help you guys with same problem!!