It could be MTU issue. These search result may help.
a.. VPN connection is disconnected after several minutes
VPN connection is disconnected after several minutes. We have been
seeing more and more cases like this one. We don't really know the causes,
....
www.chicagotech.net/VPN/vpn3minutes.htm - Similar
a.. RDC over VPN disconnects in a several minutes
3 posts - Last post: Oct 1, 2007
VPN connection is disconnected after several minutesVPN connection is
disconnected after several minutes. We have been seeing more and more ...
www.chicagotech.net/netforums/viewtopic.php?t=1309
--
Bob Lin, Microsoft-MVP, MCSE & CNE
Networking, Internet, Routing, VPN Troubleshooting on
http://www.ChicagoTech.net
How to Setup Windows, Network, VPN & Remote Access on
http://www.HowToNetworking.com
"Andrew M. Saucci, Jr." <spam-only RemoveThis @2000computer.com> wrote in message
news:%23eyZJpCVKHA.4704@TK2MSFTNGP06.phx.gbl...
> On a Windows XP laptop, I can't make a PPTP connection for ten
> minutes after restarting. Internet Explorer is working fine during that
> time; the network icon appears almost right away in the system tray. All
> of
> a sudden, after about ten minutes, without doing anything else, the PPTP
> icon starts working and is fine until shutdown. What might be causing
> this?
>
>