Thanks Justin,
 I have managed to go a little further with your ideas. But still I am not able to connect. Here is the log from syslog

Dec 30 21:51:04 sayantan-laptop NetworkManager: <info>  Starting VPN service 'org.freedesktop.NetworkManager.pptp'...
Dec 30 21:51:04 sayantan-laptop NetworkManager: <info>  VPN service 'org.freedesktop.NetworkManager.pptp' started (org.freedesktop.NetworkManager.pptp), PID 7427
Dec 30 21:51:04 sayantan-laptop NetworkManager: <info>  VPN service 'org.freedesktop.NetworkManager.pptp' just appeared, activating connections
Dec 30 21:51:04 sayantan-laptop NetworkManager: <info>  VPN plugin state changed: 3
Dec 30 21:51:04 sayantan-laptop NetworkManager: <info>  VPN connection 'office' (Connect) reply received.
Dec 30 21:51:04 sayantan-laptop pptp[7432]: nm-pptp-service-7427 log[main:pptp.c:314]: The synchronous pptp option is NOT activated
Dec 30 21:51:04 sayantan-laptop NetworkManager:    SCPlugin-Ifupdown: devices added (path: /sys/devices/virtual/net/ppp0, iface: ppp0)
Dec 30 21:51:04 sayantan-laptop NetworkManager:    SCPlugin-Ifupdown: device added (path: /sys/devices/virtual/net/ppp0, iface: ppp0): no ifupdown configuration found.
Dec 30 21:51:05 sayantan-laptop pptp[7438]: nm-pptp-service-7427 log[ctrlp_rep:pptp_ctrl.c:251]: Sent control packet type is 1 'Start-Control-Connection-Request'
Dec 30 21:51:05 sayantan-laptop pptp[7438]: nm-pptp-service-7427 log[ctrlp_disp:pptp_ctrl.c:739]: Received Start Control Connection Reply
Dec 30 21:51:05 sayantan-laptop pptp[7438]: nm-pptp-service-7427 log[ctrlp_disp:pptp_ctrl.c:773]: Client connection established.
Dec 30 21:51:06 sayantan-laptop pptp[7438]: nm-pptp-service-7427 log[ctrlp_rep:pptp_ctrl.c:251]: Sent control packet type is 7 'Outgoing-Call-Request'
Dec 30 21:51:06 sayantan-laptop pptp[7438]: nm-pptp-service-7427 log[ctrlp_disp:pptp_ctrl.c:858]: Received Outgoing Call Reply.
Dec 30 21:51:06 sayantan-laptop pptp[7438]: nm-pptp-service-7427 log[ctrlp_disp:pptp_ctrl.c:897]: Outgoing call established (call ID 0, peer's call ID 5671).
Dec 30 21:51:23 sayantan-laptop pptp[7438]: nm-pptp-service-7427 log[logecho:pptp_ctrl.c:677]: Echo Request received.
Dec 30 21:51:23 sayantan-laptop pptp[7438]: nm-pptp-service-7427 log[ctrlp_rep:pptp_ctrl.c:251]: Sent control packet type is 6 'Echo-Reply'
Dec 30 21:51:36 sayantan-laptop NetworkManager: <info>  VPN plugin failed: 1
Dec 30 21:51:36 sayantan-laptop NetworkManager:    SCPlugin-Ifupdown: devices removed (path: /sys/devices/virtual/net/ppp0, iface: ppp0)
Dec 30 21:51:36 sayantan-laptop pptp[7432]: nm-pptp-service-7427 warn[decaps_hdlc:pptp_gre.c:204]: short read (-1): Input/output error
Dec 30 21:51:36 sayantan-laptop pptp[7432]: nm-pptp-service-7427 warn[decaps_hdlc:pptp_gre.c:216]: pppd may have shutdown, see pppd log
Dec 30 21:51:36 sayantan-laptop pptp[7438]: nm-pptp-service-7427 log[callmgr_main:pptp_callmgr.c:234]: Closing connection (unhandled)
Dec 30 21:51:36 sayantan-laptop pptp[7438]: nm-pptp-service-7427 log[ctrlp_rep:pptp_ctrl.c:251]: Sent control packet type is 12 'Call-Clear-Request'
Dec 30 21:51:36 sayantan-laptop pptp[7438]: nm-pptp-service-7427 log[call_callback:pptp_callmgr.c:79]: Closing connection (call state)
Dec 30 21:51:36 sayantan-laptop NetworkManager: <info>  VPN plugin failed: 1
Dec 30 21:51:36 sayantan-laptop NetworkManager: <info>  VPN plugin state changed: 6
Dec 30 21:51:36 sayantan-laptop NetworkManager: <info>  VPN plugin state change reason: 0
Dec 30 21:51:36 sayantan-laptop NetworkManager: <WARN>  connection_state_changed(): Could not process the request because no VPN connection was active.
Dec 30 21:51:36 sayantan-laptop NetworkManager: <info>  (wlan0): writing resolv.conf to /sbin/resolvconf

Also there is no pptpd log in /var/log. How do I add it?

Thanks in Advance