I experience the same using network-manager-openconnect-gnome within Cinnamon 2.0.12. another difference in my case is, i use no certificate, but user/password-credentials to authentificate.
connecting with openconnect as suggested in comment #2 works.

here's the part of the syslog, when i fail to connect:
Nov 13 13:53:52 hostname NetworkManager[1218]: <info> logging: level 'DEBUG' domains 'PLATFORM,RFKILL,ETHER,WIFI,BT,MB,DHCP4,DHCP6,PPP,IP4,IP6,AUTOIP4,DNS,VPN,SHARING,SUPPLICANT,AGENTS,SETTINGS,SUSPEND,CORE,DEVICE,OLPC,WIMAX,INFINIBAND,FIREWALL,ADSL,BOND,VLAN,BRIDGE'
Nov 13 13:53:58 hostname NetworkManager[1218]: <info> Starting VPN service 'openconnect'...
Nov 13 13:53:58 hostname NetworkManager[1218]: <info> VPN service 'openconnect' started (org.freedesktop.NetworkManager.openconnect), PID 21155
Nov 13 13:53:58 hostname NetworkManager[1218]: <info> VPN service 'openconnect' appeared; activating connections
Nov 13 13:53:58 hostname NetworkManager[1218]: <debug> [1384347238.429080] [nm-vpn-connection.c:1413] get_secrets(): (8958a0b8-5894-4920-883e-1451d1cc8c52/vpn-provider) requesting VPN secrets pass #1
Nov 13 13:53:58 hostname NetworkManager[1218]: <debug> [1384347238.429231] [nm-agent-manager.c:1058] nm_agent_manager_get_secrets(): Secrets requested for connection /org/freedesktop/NetworkManager/Settings/0 (vpn)
Nov 13 13:53:58 hostname NetworkManager[1218]: <debug> [1384347238.429268] [nm-settings-connection.c:864] nm_settings_connection_get_secrets(): (8958a0b8-5894-4920-883e-1451d1cc8c52/vpn:1) secrets requested flags 0x80000004 hint '(null)'
Nov 13 13:53:58 hostname NetworkManager[1218]: <debug> [1384347238.429819] [nm-agent-manager.c:973] get_start(): (0x10e6a50/vpn) system settings secrets sufficient
Nov 13 13:53:58 hostname NetworkManager[1218]: <debug> [1384347238.429841] [nm-settings-connection.c:721] agent_secrets_done_cb(): (8958a0b8-5894-4920-883e-1451d1cc8c52/vpn:1) existing secrets returned
Nov 13 13:53:58 hostname NetworkManager[1218]: <debug> [1384347238.429852] [nm-settings-connection.c:727] agent_secrets_done_cb(): (8958a0b8-5894-4920-883e-1451d1cc8c52/vpn:1) secrets request completed
Nov 13 13:53:58 hostname NetworkManager[1218]: <debug> [1384347238.431959] [nm-settings-connection.c:767] agent_secrets_done_cb(): (8958a0b8-5894-4920-883e-1451d1cc8c52/vpn:1) new agent secrets processed
Nov 13 13:53:58 hostname NetworkManager[1218]: <debug> [1384347238.431995] [nm-vpn-connection.c:1379] get_secrets_cb(): (8958a0b8-5894-4920-883e-1451d1cc8c52/vpn-provider) asking service if additional secrets are required
Nov 13 13:53:58 hostname NetworkManager[1218]: <info> VPN plugin state changed: init (1)
Nov 13 13:53:58 hostname NetworkManager[1218]: <debug> [1384347238.433939] [nm-vpn-connection.c:1340] plugin_need_secrets_cb(): (8958a0b8-5894-4920-883e-1451d1cc8c52/vpn-provider) service indicated additional secrets required
Nov 13 13:53:58 hostname NetworkManager[1218]: <debug> [1384347238.433986] [nm-vpn-connection.c:1413] get_secrets(): (8958a0b8-5894-4920-883e-1451d1cc8c52/vpn-provider) requesting VPN secrets pass #2
Nov 13 13:53:58 hostname NetworkManager[1218]: <debug> [1384347238.434133] [nm-agent-manager.c:1058] nm_agent_manager_get_secrets(): Secrets requested for connection /org/freedesktop/NetworkManager/Settings/0 (vpn)
Nov 13 13:53:58 hostname NetworkManager[1218]: <debug> [1384347238.434364] [nm-agent-manager.c:577] request_add_agent(): (:1.53/org.freedesktop.nm-applet/1000) agent allowed for secrets request 0x10e7870/vpn
Nov 13 13:53:58 hostname NetworkManager[1218]: <debug> [1384347238.434398] [nm-settings-connection.c:864] nm_settings_connection_get_secrets(): (8958a0b8-5894-4920-883e-1451d1cc8c52/vpn:2) secrets requested flags 0x4 hint '(null)'
Nov 13 13:53:58 hostname NetworkManager[1218]: <debug> [1384347238.434798] [nm-agent-manager.c:979] get_start(): (0x10e7870/vpn) system settings secrets insufficient, asking agents
Nov 13 13:53:58 hostname NetworkManager[1218]: <debug> [1384347238.434814] [nm-agent-manager.c:652] next_generic(): (:1.53/org.freedesktop.nm-applet/1000) agent getting secrets for request 0x10e7870/vpn
Nov 13 13:53:58 hostname NetworkManager[1218]: <debug> [1384347238.434823] [nm-agent-manager.c:912] get_next_cb(): (0x10e7870/vpn) request has system secrets; checking agent :1.53 for MODIFY
Nov 13 13:53:58 hostname NetworkManager[1218]: <debug> [1384347238.438855] [nm-agent-manager.c:843] get_agent_modify_auth_cb(): (0x10e7870/vpn) agent MODIFY check result 1
Nov 13 13:53:58 hostname NetworkManager[1218]: <debug> [1384347238.476972] [nm-agent-manager.c:719] get_done_cb(): (:1.53/org.freedesktop.nm-applet/1000) agent returned secrets for request 0x10e7870/vpn
Nov 13 13:53:58 hostname NetworkManager[1218]: <debug> [1384347238.477112] [nm-settings-connection.c:684] agent_secrets_done_cb(): (8958a0b8-5894-4920-883e-1451d1cc8c52/vpn:2) secrets returned from agent :1.53
Nov 13 13:53:58 hostname NetworkManager[1218]: <debug> [1384347238.477125] [nm-settings-connection.c:727] agent_secrets_done_cb(): (8958a0b8-5894-4920-883e-1451d1cc8c52/vpn:2) secrets request completed
Nov 13 13:53:58 hostname NetworkManager[1218]: <debug> [1384347238.477921] [nm-settings-connection.c:767] agent_secrets_done_cb(): (8958a0b8-5894-4920-883e-1451d1cc8c52/vpn:2) new agent secrets processed
Nov 13 13:53:58 hostname NetworkManager[1218]: <debug> [1384347238.477939] [nm-vpn-connection.c:1379] get_secrets_cb(): (8958a0b8-5894-4920-883e-1451d1cc8c52/vpn-provider) asking service if additional secrets are required
Nov 13 13:53:58 hostname NetworkManager[1218]: <debug> [1384347238.479366] [nm-vpn-connection.c:1340] plugin_need_secrets_cb(): (8958a0b8-5894-4920-883e-1451d1cc8c52/vpn-provider) service indicated additional secrets required
Nov 13 13:53:58 hostname NetworkManager[1218]: <debug> [1384347238.479397] [nm-vpn-connection.c:1413] get_secrets(): (8958a0b8-5894-4920-883e-1451d1cc8c52/vpn-provider) requesting VPN secrets pass #3
Nov 13 13:53:58 hostname NetworkManager[1218]: <debug> [1384347238.479464] [nm-agent-manager.c:1058] nm_agent_manager_get_secrets(): Secrets requested for connection /org/freedesktop/NetworkManager/Settings/0 (vpn)
Nov 13 13:53:58 hostname NetworkManager[1218]: <debug> [1384347238.479587] [nm-agent-manager.c:577] request_add_agent(): (:1.53/org.freedesktop.nm-applet/1000) agent allowed for secrets request 0x10ee020/vpn
Nov 13 13:53:58 hostname NetworkManager[1218]: <debug> [1384347238.479607] [nm-settings-connection.c:864] nm_settings_connection_get_secrets(): (8958a0b8-5894-4920-883e-1451d1cc8c52/vpn:3) secrets requested flags 0x5 hint '(null)'
Nov 13 13:53:58 hostname NetworkManager[1218]: <debug> [1384347238.479898] [nm-agent-manager.c:979] get_start(): (0x10ee020/vpn) system settings secrets insufficient, asking agents
Nov 13 13:53:58 hostname NetworkManager[1218]: <debug> [1384347238.479912] [nm-agent-manager.c:652] next_generic(): (:1.53/org.freedesktop.nm-applet/1000) agent getting secrets for request 0x10ee020/vpn
Nov 13 13:53:58 hostname NetworkManager[1218]: <debug> [1384347238.479919] [nm-agent-manager.c:912] get_next_cb(): (0x10ee020/vpn) request has system secrets; checking agent :1.53 for MODIFY
Nov 13 13:53:58 hostname NetworkManager[1218]: <debug> [1384347238.486329] [nm-agent-manager.c:843] get_agent_modify_auth_cb(): (0x10ee020/vpn) agent MODIFY check result 1
Nov 13 13:54:22 hostname NetworkManager[1218]: <debug> [1384347262.940321] [nm-agent-manager.c:719] get_done_cb(): (:1.53/org.freedesktop.nm-applet/1000) agent returned secrets for request 0x10ee020/vpn
Nov 13 13:54:22 hostname NetworkManager[1218]: <debug> [1384347262.940534] [nm-settings-connection.c:684] agent_secrets_done_cb(): (8958a0b8-5894-4920-883e-1451d1cc8c52/vpn:3) secrets returned from agent :1.53
Nov 13 13:54:22 hostname NetworkManager[1218]: <debug> [1384347262.940612] [nm-settings-connection.c:727] agent_secrets_done_cb(): (8958a0b8-5894-4920-883e-1451d1cc8c52/vpn:3) secrets request completed
Nov 13 13:54:22 hostname NetworkManager[1218]: <debug> [1384347262.942948] [nm-settings-connection.c:760] agent_secrets_done_cb(): (8958a0b8-5894-4920-883e-1451d1cc8c52/vpn:3) saving new secrets to backing storage
Nov 13 13:54:22 hostname NetworkManager[1218]: <debug> [1384347262.947386] [nm-vpn-connection.c:1379] get_secrets_cb(): (8958a0b8-5894-4920-883e-1451d1cc8c52/vpn-provider) asking service if additional secrets are required
Nov 13 13:54:22 hostname NetworkManager[1218]: <debug> [1384347262.953937] [nm-vpn-connection.c:1349] plugin_need_secrets_cb(): (8958a0b8-5894-4920-883e-1451d1cc8c52/vpn-provider) service indicated no additional secrets required
Nov 13 13:54:22 hostname NetworkManager[1218]: <debug> [1384347262.958106] [nm-ip6-manager.c:1340] netlink_notification(): netlink event type 16
Nov 13 13:54:22 hostname NetworkManager[1218]: <debug> [1384347262.958137] [nm-ip6-manager.c:1301] process_newlink(): ignoring netlink message family 0
Nov 13 13:54:22 hostname NetworkManager[1218]: <debug> [1384347262.958176] [nm-netlink-monitor.c:164] link_msg_handler(): netlink link message: iface idx 4 flags 0x1090
Nov 13 13:54:22 hostname NetworkManager[1218]: <info> VPN plugin state changed: starting (3)
Nov 13 13:54:22 hostname NetworkManager[1218]:    SCPlugin-Ifupdown: devices added (path: /sys/devices/virtual/net/vpn0, iface: vpn0)
Nov 13 13:54:22 hostname NetworkManager[1218]:    SCPlugin-Ifupdown: device added (path: /sys/devices/virtual/net/vpn0, iface: vpn0): no ifupdown configuration found.
Nov 13 13:54:22 hostname NetworkManager[1218]: <debug> [1384347262.959198] [nm-udev-manager.c:563] handle_uevent(): UDEV event: action 'add' subsys 'net' device 'vpn0'
Nov 13 13:54:22 hostname NetworkManager[1218]: <warn> /sys/devices/virtual/net/vpn0: couldn't determine device driver; ignoring...
Nov 13 13:54:22 hostname NetworkManager[1218]: <debug> [1384347262.959427] [nm-udev-manager.c:216] recheck_killswitches(): WiFi rfkill switch rfkill0 state now 0/1
Nov 13 13:54:22 hostname NetworkManager[1218]: <info> VPN connection 'vpn-provider' (Connect) reply received.
Nov 13 13:54:23 hostname openconnect[21555]: Verbindungsversuch mit Server 130.149.5.50:443
Nov 13 13:54:23 hostname openconnect[21555]: SSL-Verhandlung mit vpn.provider.com
Nov 13 13:54:23 hostname openconnect[21555]: Verbunden mit HTTPS auf vpn.provider.com
Nov 13 13:54:23 hostname openconnect[21555]: Unpassende HTTP CONNECT-Antwort erhalten: HTTP/1.1 401 Unauthorized
Nov 13 13:54:23 hostname avahi-daemon[1213]: Withdrawing workstation service for vpn0.
Nov 13 13:54:23 hostname NetworkManager[1218]: <debug> [1384347263.397130] [nm-ip6-manager.c:1340] netlink_notification(): netlink event type 17
Nov 13 13:54:23 hostname NetworkManager[1218]: <debug> [1384347263.397341] [nm-netlink-monitor.c:164] link_msg_handler(): netlink link message: iface idx 4 flags 0x1090
Nov 13 13:54:23 hostname NetworkManager[1218]:    SCPlugin-Ifupdown: devices removed (path: /sys/devices/virtual/net/vpn0, iface: vpn0)
Nov 13 13:54:23 hostname NetworkManager[1218]: <debug> [1384347263.398846] [nm-udev-manager.c:563] handle_uevent(): UDEV event: action 'remove' subsys 'net' device 'vpn0'
Nov 13 13:54:23 hostname NetworkManager[1218]: <debug> [1384347263.399048] [nm-udev-manager.c:216] recheck_killswitches(): WiFi rfkill switch rfkill0 state now 0/1
Nov 13 13:54:23 hostname NetworkManager[1218]: <warn> VPN plugin failed: 0
Nov 13 13:54:23 hostname NetworkManager[1218]: <info> VPN plugin state changed: stopped (6)
Nov 13 13:54:23 hostname NetworkManager[1218]: <info> VPN plugin state change reason: 10
Nov 13 13:54:23 hostname NetworkManager[1218]: <debug> [1384347263.427566] [nm-dns-manager.c:1017] nm_dns_manager_begin_updates(): (vpn_connection_deactivated): queueing DNS updates (1)
Nov 13 13:54:23 hostname NetworkManager[1218]: <debug> [1384347263.427586] [nm-dns-manager.c:1017] nm_dns_manager_begin_updates(): (update_routing_and_dns): queueing DNS updates (2)
Nov 13 13:54:23 hostname NetworkManager[1218]: <info> Policy set 'Kabelnetzwerkverbindung 1' (eth0) as default for IPv4 routing and DNS.
Nov 13 13:54:23 hostname NetworkManager[1218]: <debug> [1384347263.427817] [nm-dns-manager.c:1035] nm_dns_manager_end_updates(): (nm_dns_manager_end_updates): DNS configuration did not change
Nov 13 13:54:23 hostname NetworkManager[1218]: <debug> [1384347263.427833] [nm-dns-manager.c:1039] nm_dns_manager_end_updates(): (update_routing_and_dns): no DNS changes to commit (1)
Nov 13 13:54:23 hostname NetworkManager[1218]: <debug> [1384347263.427856] [nm-dns-manager.c:1035] nm_dns_manager_end_updates(): (nm_dns_manager_end_updates): DNS configuration did not change
Nov 13 13:54:23 hostname NetworkManager[1218]: <debug> [1384347263.427869] [nm-dns-manager.c:1039] nm_dns_manager_end_updates(): (vpn_connection_deactivated): no DNS changes to commit (0)
Nov 13 13:54:23 hostname NetworkManager[1218]: <debug> [1384347263.427890] [nm-policy.c:1008] process_secondaries(): Secondary connection 'vpn-provider' FAILED; active path '/org/freedesktop/NetworkManager/ActiveConnection/1'
Nov 13 13:54:23 hostname NetworkManager[1218]: <warn> error disconnecting VPN: Could not process the request because no VPN connection was active.
Nov 13 13:54:23 hostname NetworkManager[1218]:    keyfile: updating /etc/NetworkManager/system-connections/vpn-provider
Nov 13 13:54:29 hostname NetworkManager[1218]: <info> VPN service 'openconnect' disappeared
Nov 13 13:54:31 hostname NetworkManager[1218]: <debug> [1384347271.140889] [nm-vpn-service.c:274] ensure_killed(): waiting for VPN service pid 21155 to exit
Nov 13 13:54:31 hostname NetworkManager[1218]: <debug> [1384347271.140988] [nm-vpn-service.c:276] ensure_killed(): VPN service pid 21155 cleaned up