After some tinkering I've found a somewhat different workaround (of you might call it a fix) and a probable immediate cause of this behavior.
My VPN server has an address of 192.168.17.1 and it assings a range 192.168.17.33 - 192.168.17.62 to clients. I used to manually add the following routes (this is supposed to like the relevant dialog): Address Netmask Gateway Metric 192.168.17.0 255.255.255.0 192.168.17.1 1 172.16.32.0 255.255.252.0 192.168.17.1 1 This did work because (I believe, cannot really bother with testing now) Network Manager or PPTP plugin added a route to the VPN gateway (192.168.17.1 in my case). And it no longer does. Without this route further routes are considered invalid. This here might be a bug or it might have been redesigned — I don't know. Luckily there is way to enter link scoped routes in that dialog, although unintuitive: you just leave the "Gateway" field empty. Like this: Address Netmask Gateway Metric 192.168.17.0 255.255.255.0 1 172.16.32.0 255.255.252.0 1 The "OK" button turns inactive after you delete a gateway, so you have to tab or click some other field for it to come back. After this the connection works and the following routes get added to the routing table: > ip route default ... <vpn gateway external ip> via <your usual first hop router> ... 172.16.32.0/22 dev ppp0 proto static scope link metric 1 192.168.17.0/24 dev ppp0 proto static scope link metric 1 192.168.17.35 dev ppp0 proto kernel scope link src 192.168.17.35 metric 50 ... Hope this helps someone else -- You received this bug notification because you are a member of Desktop Packages, which is subscribed to network-manager-pptp in Ubuntu. https://bugs.launchpad.net/bugs/1511330 Title: PPTP connection does not establish due to error: "Connection activation failed: the VPN service returned invalid configuration." Status in network-manager-pptp package in Ubuntu: Confirmed Bug description: The PPTP connection in question used to work on Vivid, now it does not connect after an upgrade to Wily. That error description in the title comes from nmcli; it looks somewhat different in the notification popup The relevant piece of syslog is in the attached syslog-snippet.txt I'd say that the IP config as stated in the log looks valid to me ProblemType: Bug DistroRelease: Ubuntu 15.10 Package: network-manager-pptp 0.9.10.0-1ubuntu1 ProcVersionSignature: Ubuntu 4.2.0-16.19-generic 4.2.3 Uname: Linux 4.2.0-16-generic x86_64 ApportVersion: 2.19.1-0ubuntu4 Architecture: amd64 CurrentDesktop: Unity Date: Thu Oct 29 14:07:01 2015 InstallationDate: Installed on 2015-08-20 (69 days ago) InstallationMedia: Ubuntu 15.04 "Vivid Vervet" - Release amd64 (20150422) SourcePackage: network-manager-pptp UpgradeStatus: No upgrade log present (probably fresh install) To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/network-manager-pptp/+bug/1511330/+subscriptions -- Mailing list: https://launchpad.net/~desktop-packages Post to : desktop-packages@lists.launchpad.net Unsubscribe : https://launchpad.net/~desktop-packages More help : https://help.launchpad.net/ListHelp