VPN loses connection after 2 minutes

Hi

I have three Win XP boxes, one is set up as a VPN host, the other as a
VPN client, which is on a separate network. Both are permanently
connect to the internet.

Able to connect to the host from the client and browse shared folders
on the host.

However, every time I connect the connection always drops after 2 min
18 sec, whether I am browsing or not.

Does anyone have any ideas how to solve this problem?