PPTP Disconnects Every 3 Min.

Here's a curious issue:

One of our clients is VPNing into their client's network via PPTP connection. They're kicked off every three minutes.

So we got the WAN IP to connect to and the user/pass to login. VPNed in and started running a continuous ping, and sure enough, everything dropped in exactly three minutes. We can reconnect, but then we're kicked off precisely three minutes later again.

Googling the issue, we're finding that a number of people are having the same problem, but few actually have a resolution for it. It seems that perhaps a particular Windows hotfix may resolve the problem, but I'm not sure.

Unfortunately, since the network in question is the client of a client, that's all the info I have to work with thus far, so I'm pretty limited. But has anyone encountered this issue before? Both we and our client use PIXes, but I have no idea what kind of router/firewall the destination network is running.

Has anyone done a packet sniff and checked what's happening to packets around 2:45-3:10?