I had two problem with my pptp vpn connection on ubuntu 14.04 with 3.19 Kernel.
first it wont connect at all and i solved that with this command:
sudo modprobe nf_conntrack_pptp nf_conntrack_proto_gre
second my vpn connection gets disconnected after a few second (usually with first packets transmit) and i solved that with my vpn setting's on network manager: IPv4 Setting tab -> Routers -> checked both check boxes there.
I had two problem with my pptp vpn connection on ubuntu 14.04 with 3.19 Kernel.
first it wont connect at all and i solved that with this command:
sudo modprobe nf_conntrack_pptp nf_conntrack_ proto_gre
second my vpn connection gets disconnected after a few second (usually with first packets transmit) and i solved that with my vpn setting's on network manager:
IPv4 Setting tab -> Routers -> checked both check boxes there.