Advice on constant VPN connection fails (Win7 -> Ubuntu 11.04)

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http://serverfault.com – I've set up a VPN to allow me to access work files from home, but I'm having constant connection issues. Home machine: Windows 7 Home Premium (v6.1, build 7600) Home router: SpeedTouch 780, firmware Work machine: Ubuntu Server 11.04 running pptpd Work router: Thomson Gateway TG585 v7, firmware From my machine at work I can make a VPN connection across the network with no problems. From home I can connect, but the majority of the time the connection drops within a few seconds. I've had it stable once (enough to use Putty to issue a few commands) and I can access web sites on t (HowTos)