Poptop GRE read error

[Cromwell]

Hi

I'm having trouble setting up a VPN to connect my pc to. Now I'm able to connect to the VPN and the internet throught it, but the connection fails after a few minutes.

pptpd v1.3.4
Linux 2.6.18
Debian 5.0

Oct 24 20:50:10 64456 pptpd[8443]: CTRL: Client client_ip control connection started
Oct 24 20:50:10 64456 pptpd[8443]: CTRL: Starting call (launching pppd, opening GRE)
Oct 24 20:50:10 64456 pptpd[8443]: GRE: Bad checksum from pppd.
Oct 24 20:50:11 64456 pptpd[8443]: CTRL: Ignored a SET LINK INFO packet with real ACCMs!
Oct 24 20:52:32 64456 pptpd[8443]: GRE: read(fd=7,buffer=80505a0,len=8260) from network failed: status = -1 error = Protocol not available
Oct 24 20:52:32 64456 pptpd[8443]: CTRL: GRE read or PTY write failed (gre,pty)=(7,6)
Oct 24 20:52:32 64456 pptpd[8443]: CTRL: Reaping child PPP[8444]
Oct 24 20:52:32 64456 pptpd[8443]: CTRL: Client client_ip control connection finished

Oct 24 20:48:50 64456 kernel: GRE over IPv4 tunneling driver
Oct 24 20:50:10 64456 pppd[8444]: Plugin /usr/lib/pptpd/pptpd-logwtmp.so loaded.
Oct 24 20:50:10 64456 pppd[8444]: pptpd-logwtmp: $Version$
Oct 24 20:50:10 64456 pppd[8444]: pppd 2.4.4 started by root, uid 0
Oct 24 20:50:10 64456 pppd[8444]: Using interface ppp0
Oct 24 20:50:10 64456 pppd[8444]: Connect: ppp0 <--> /dev/pts/1
Oct 24 20:50:11 64456 pppd[8444]: MPPE 128-bit stateless compression enabled
Oct 24 20:50:13 64456 pppd[8444]: local  IP address 192.168.0.1
Oct 24 20:50:13 64456 pppd[8444]: remote IP address 192.168.1.1
Oct 24 20:50:13 64456 pppd[8444]: pptpd-logwtmp.so ip-up ppp0 client_username client_ip
Oct 24 20:52:32 64456 pppd[8444]: Modem hangup
Oct 24 20:52:32 64456 pppd[8444]: pptpd-logwtmp.so ip-down ppp0
Oct 24 20:52:32 64456 pppd[8444]: Connect time 2.4 minutes.
Oct 24 20:52:32 64456 pppd[8444]: Sent 227248 bytes, received 124995 bytes.
Oct 24 20:52:32 64456 pppd[8444]: Connection terminated.
Oct 24 20:52:32 64456 pppd[8444]: Exit.
Oct 24 21:11:44 64456 -- MARK --

There is an explanation of this error at poptop.sourceforge[net]/dox/qna.html#27

As it suggested, I installed tcpdump and ran the following: (binary)

tcpdump -w test.pcap \(dst client_ip or src client_ip\) and \(icmp port 22 or icmp port 1723\)

I also ran "modprobe ip_nat_pptp" just in case it wasn't loaded.

Not sure what I should do?
Thanks-

[Cromwell]

Overdue update:
Turn on Windows firewall (Vista)