I also have two clients that are using the BEFSR41, as well, and they cannot get threw on there wireless connections. Is it some setting on the router on the WLAN side? We are using the 3000 concentrator, and everyone VPN'ing from home that does not use a router/firewall connects fine. My Dlink 713P (wireless) at home, works great on the VPN and it has never given me a hard time. I have never messed around with the settings on the router, other then to enable MAC address control. Otherwise there is no WEP encryption enabled, or any other security methods. All three routers are DHCP in and out, and all clients are win2k machines running 3.6.1.
I know this is not an answer, but i wanted to ask the same question, and give a little bit more insight on it.
Thanks