Comment 5 for bug 290178

I'm having the same issue. I can connect, but sooner or later (usually sooner) the connection will drop. I have tried adjusting my MTU to various sizes, but this doesn't help. I have Windows 7 and Mac OSX running on the same computer, and the VPN connection within those operating systems is stable and reliable (stays connected for weeks).

Here is my /var/log/syslog report of the disconnection:

Oct 10 05:44:27 iMac-Ubuntu pptp[11871]: nm-pptp-service-11745 log[pptp_read_some:pptp_ctrl.c:544]: read returned zero, peer has closed
Oct 10 05:44:27 iMac-Ubuntu pptp[11871]: nm-pptp-service-11745 log[callmgr_main:pptp_callmgr.c:258]: Closing connection (shutdown)
Oct 10 05:44:27 iMac-Ubuntu pptp[11871]: nm-pptp-service-11745 log[ctrlp_rep:pptp_ctrl.c:251]: Sent control packet type is 12 'Call-Clear-Request'
Oct 10 05:44:27 iMac-Ubuntu pptp[11871]: nm-pptp-service-11745 log[pptp_read_some:pptp_ctrl.c:544]: read returned zero, peer has closed
Oct 10 05:44:27 iMac-Ubuntu pptp[11871]: nm-pptp-service-11745 log[call_callback:pptp_callmgr.c:79]: Closing connection (call state)
Oct 10 05:44:27 iMac-Ubuntu pppd[11861]: Modem hangup
Oct 10 05:44:27 iMac-Ubuntu pppd[11861]: Connect time 22.6 minutes.
Oct 10 05:44:27 iMac-Ubuntu pppd[11861]: Sent 36219320 bytes, received 1371467319 bytes.
Oct 10 05:44:27 iMac-Ubuntu pppd[11861]: MPPE disabled
Oct 10 05:44:27 iMac-Ubuntu pppd[11861]: Connection terminated.
Oct 10 05:44:27 iMac-Ubuntu NetworkManager[806]: <info> VPN plugin state changed: 5
Oct 10 05:44:27 iMac-Ubuntu NetworkManager[806]: <info> VPN plugin state changed: 6
Oct 10 05:44:27 iMac-Ubuntu NetworkManager[806]: <info> VPN plugin state change reason: 0
Oct 10 05:44:27 iMac-Ubuntu NetworkManager[806]: <warn> error disconnecting VPN: Could not process the request because no VPN connection was active.
Oct 10 05:44:27 iMac-Ubuntu pppd[11861]: Terminating on signal 15
Oct 10 05:44:27 iMac-Ubuntu pppd[11861]: Exit.
Oct 10 05:44:28 iMac-Ubuntu NetworkManager[806]: <info> Policy set 'Auto eth0' (eth0) as default for IPv4 routing and DNS.
Oct 10 05:44:28 iMac-Ubuntu NetworkManager[806]: SCPlugin-Ifupdown: devices removed (path: /sys/devices/virtual/net/ppp0, iface: ppp0)
Oct 10 05:44:33 iMac-Ubuntu NetworkManager[806]: <info> VPN service 'pptp' disappeared

I have spoken to my systems administrator, and he says:

"According to our debug log the disconnections are caused by malformed GRE packets. We have a lot of bad checksums on your connection."

The connection is a PPTP, configured via Network Manager.