Ubuntu 16.04 LTS. OpenVPN having issue

Jan 16 11:18:47 jaguar-GL552VX gnome-session[1705]: ** Message: vpn: (iodine,/etc/NetworkManager/VPN/nm-iodine-service.name) cannot load legacy-only plugin
Jan 16 11:18:47 jaguar-GL552VX gnome-session[1705]: ** Message: vpn: (strongswan,/etc/NetworkManager/VPN/nm-strongswan-service.name) cannot load legacy-only plugin
Jan 16 11:18:47 jaguar-GL552VX gnome-session[1705]: Gtk-Message: GtkDialog mapped without a transient parent. This is discouraged.
Jan 16 11:18:52 jaguar-GL552VX gnome-session[1705]: Gtk-Message: GtkDialog mapped without a transient parent. This is discouraged.
Jan 16 11:18:52 jaguar-GL552VX dbus[863]: [system] Activating via systemd: service name='org.freedesktop.hostname1' unit='dbus-org.freedesktop.hostname1.service'
Jan 16 11:18:52 jaguar-GL552VX systemd[1]: Starting Hostname Service...
Jan 16 11:18:52 jaguar-GL552VX dbus[863]: [system] Successfully activated service 'org.freedesktop.hostname1'
Jan 16 11:18:52 jaguar-GL552VX systemd[1]: Started Hostname Service.
Jan 16 11:19:01 jaguar-GL552VX gnome-session[1705]: Gtk-Message: GtkDialog mapped without a transient parent. This is discouraged.

probably caused by Bug #1578193

What is the output:

lsb_release -a; uname -a; apt-cache policy openvpn

Thanks

No LSB modules are available.
Distributor ID: Ubuntu
Description: Ubuntu 16.04.3 LTS
Release: 16.04
Codename: xenial
Linux jaguar-Aspire-V3-571G 4.13.0-26-generic #29~16.04.2-Ubuntu SMP Tue Jan 9 22:00:44 UTC 2018 x86_64 x86_64 x86_64 GNU/Linux
openvpn:
  Installed: 2.3.10-1ubuntu2.1
  Candidate: 2.3.10-1ubuntu2.1
  Version table:
 *** 2.3.10-1ubuntu2.1 500
        500 http://in.archive.ubuntu.com/ubuntu xenial-updates/main amd64 Packages
        500 http://security.ubuntu.com/ubuntu xenial-security/main amd64 Packages
        100 /var/lib/dpkg/status
     2.3.10-1ubuntu2 500
        500 http://in.archive.ubuntu.com/ubuntu xenial/main amd64 Packages

no one knows how to fix this issue??

For diagnostic purposes, what is the output of the command

apt-cache policy strongswan network-manager-strongswan iodine network-manager-iodine network-manager

You wrote "Working for a long time until recently."
Can you indicate when it stopped working, and what there was done at that time (maybe installation of package updates)?

i reinstalled the os 5days back because it was throwing some graphic card error on login and i was not able to login at that time.

Output of the command is pasted below:

strongswan:
  Installed: (none)
  Candidate: 5.3.5-1ubuntu3.5
  Version table:
     5.3.5-1ubuntu3.5 500
        500 http://in.archive.ubuntu.com/ubuntu xenial-updates/main amd64 Packages
        500 http://in.archive.ubuntu.com/ubuntu xenial-updates/main i386 Packages
     5.3.5-1ubuntu3.4 500
        500 http://security.ubuntu.com/ubuntu xenial-security/main amd64 Packages
        500 http://security.ubuntu.com/ubuntu xenial-security/main i386 Packages
     5.3.5-1ubuntu3 500
        500 http://in.archive.ubuntu.com/ubuntu xenial/main amd64 Packages
        500 http://in.archive.ubuntu.com/ubuntu xenial/main i386 Packages
network-manager-strongswan:
  Installed: 1.3.1-1ubuntu1
  Candidate: 1.3.1-1ubuntu1
  Version table:
 *** 1.3.1-1ubuntu1 500
        500 http://in.archive.ubuntu.com/ubuntu xenial/universe amd64 Packages
        100 /var/lib/dpkg/status
iodine:
  Installed: 0.7.0-4
  Candidate: 0.7.0-4
  Version table:
 *** 0.7.0-4 500
        500 http://in.archive.ubuntu.com/ubuntu xenial/universe amd64 Packages
        100 /var/lib/dpkg/status
network-manager-iodine:
  Installed: 0.0.5-1ubuntu1
  Candidate: 0.0.5-1ubuntu1
  Version table:
 *** 0.0.5-1ubuntu1 500
        500 http://in.archive.ubuntu.com/ubuntu xenial/universe amd64 Packages
        100 /var/lib/dpkg/status
network-manager:
  Installed: 1.2.6-0ubuntu0.16.04.2
  Candidate: 1.2.6-0ubuntu0.16.04.2
  Version table:
 *** 1.2.6-0ubuntu0.16.04.2 500
        500 http://in.archive.ubuntu.com/ubuntu xenial-updates/main amd64 Packages
        100 /var/lib/dpkg/status
     1.2.2-0ubuntu0.16.04.4 500
        500 http://security.ubuntu.com/ubuntu xenial-security/main amd64 Packages
     1.1.93-0ubuntu4 500
        500 http://in.archive.ubuntu.com/ubuntu xenial/main amd64 Packages

This seems to be Bug #1578193 (see especially its duplicate Bug #1588862 )

If the previous system has worked well, and after new installation it does no more, then you seem to have set up your new system in a somewhat different configuration. Do you have any idea what the difference is to your previous system? Maybe you can change your new system back to what the old one had, and vpn will work again?