VPN connection prompt

Hello,

I have a laptop running Vista Ultimate. When I'm at home, I connect to my
home network via wi-fi, but when I'm out and about, I connect via a VPN over
either someone else's wi-fi, or GPRS/3G.

The problem I have is that occationally, when I'm browsing the web at home,
my VPN connection prompt window automatically pops up. It shouldn't because
I'm already connected to my network and gateway. While the VPN connection
window is displayed, I have no network access, as soon as I click cancel,
the local network returns.

As a temp fix, I've deleted the VPN connection. It's pretty easy for me to
recreate it as and when I need it, but of course this isn't ideal. Is there
anyway I can either stop this from happening, or simply set the VPN
connection as disabled (rather than delete it). I've tried playing the the
TCP metrics, but this has no effect.

Thanks.