I had the same Problem 2 years ago. All worked fine (other games, applications etc), only in LFS i couldn´t connect to any host. Hosting an own server was no problem and after configuring the Fritzbox as an modem, joining to an host also runs, but with the fritzbox configured as a router, i always had the error message. I had tested everything, called hotlines from avm....... at last i installed a new network card - and disabled the onboard on my Asus-Board - first start - and it runs. Since this time i never had this Problem.