vpn service fails

Trying to connect via VPN (pptp) fails:

Mar 31 12:25:39 mbr NetworkManager[1002]: <info> Starting VPN service 'pptp'...
Mar 31 12:25:39 mbr NetworkManager[1002]: <info> VPN service 'pptp' started (org.freedesktop.NetworkManager.pptp), PID 4143
Mar 31 12:25:39 mbr NetworkManager[1002]: <info> VPN service 'pptp' appeared; activating connections
Mar 31 12:25:39 mbr NetworkManager[1002]: <error> [1427797539.109043] [nm-vpn-connection.c:1374] get_secrets_cb(): Failed to request VPN secrets #2: (6) No agents were available for this request.
Mar 31 12:25:39 mbr NetworkManager[1002]: <info> Policy set 'rsb_hs' (wlan0) as default for IPv4 routing and DNS.
Mar 31 12:25:43 mbr NetworkManager[1002]: <info> VPN service 'pptp' disappeared

Workaround (as previously suggested):

remove ~/.gconf/apps/nm-applet/%gconf.xml
logout / login
connection works

...
until the next reboot

System: Ubuntu 14.10 (64bit)
Linux mbr 3.16.0-34-generic #45-Ubuntu SMP Mon Mar 23 17:21:27 UTC 2015 x86_64 x86_64 x86_64 GNU/Linux

Not quite similar to #1297849 but same effect.

ProblemType: Bug
DistroRelease: Ubuntu 14.10
Package: network-manager 0.9.8.8-0ubuntu28
ProcVersionSignature: Ubuntu 3.16.0-34.45-generic 3.16.7-ckt8
Uname: Linux 3.16.0-34-generic x86_64
NonfreeKernelModules: nvidia wl
ApportVersion: 2.14.7-0ubuntu8.2
Architecture: amd64
Date: Tue Mar 31 12:27:16 2015
IfupdownConfig:
 # interfaces(5) file used by ifup(8) and ifdown(8)
 auto lo
 iface lo inet loopback
InstallationDate: Installed on 2013-05-17 (682 days ago)
InstallationMedia: Ubuntu 13.04 "Raring Ringtail" - Release amd64+mac (20130424)
IpRoute:
 default via 10.1.0.254 dev wlan0 proto static
 10.0.0.0/8 dev wlan0 proto kernel scope link src 10.1.0.103 metric 9
 192.168.97.0/24 dev vmnet8 proto kernel scope link src 192.168.97.1
 192.168.204.0/24 dev vmnet1 proto kernel scope link src 192.168.204.1
NetworkManager.state:
 [main]
 NetworkingEnabled=true
 WirelessEnabled=true
 WWANEnabled=true
 WimaxEnabled=true
SourcePackage: network-manager
UpgradeStatus: No upgrade log present (probably fresh install)
nmcli-dev:
 DEVICE TYPE STATE DBUS-PATH
 EC:88:92:61:E9:5F bluetooth disconnected /org/freedesktop/NetworkManager/Devices/1
 wlan0 802-11-wireless connected /org/freedesktop/NetworkManager/Devices/0
nmcli-nm:
 RUNNING VERSION STATE NET-ENABLED WIFI-HARDWARE WIFI WWAN-HARDWARE WWAN
 running 0.9.8.8 connected enabled enabled enabled enabled disabled