No response to PAP authenticate-requests

Hi Dear Developer,

After reboot my laptop, the problem regarding timeout of xl2tpd seemed had gone. This time it looks like I am very close to a successful connection, because there are no "red" text in the detailed information! However, it still need some fix. Below is the log:
===================================================================
ipsec_setup: Starting Openswan IPsec U2.6.28/K3.0.0-12-generic...
Nov 14 12:58:39 jackxu-hp ipsec__plutorun: Starting Pluto subsystem...
Nov 14 12:58:39 jackxu-hp ipsec__plutorun: adjusting ipsec.d to /etc/ipsec.d
recvref[22]: Protocol not available
xl2tpd[3730]: This binary does not support kernel L2TP.
Starting xl2tpd: xl2tpd.
xl2tpd[3731]: xl2tpd version xl2tpd-1.2.8 started on jackxu-hp PID:3731
xl2tpd[3731]: Written by Mark Spencer, Copyright (C) 1998, Adtran, Inc.
xl2tpd[3731]: Forked by Scott Balmos and David Stipp, (C) 2001
xl2tpd[3731]: Inherited by Jeff McAdams, (C) 2002
xl2tpd[3731]: Forked again by Xelerance (www.xelerance.com) (C) 2006
xl2tpd[3731]: Listening on IP address 0.0.0.0, port 1701
Nov 14 12:58:39 jackxu-hp ipsec__plutorun: 002 added connection description "CUHKVPN"
Nov 14 12:58:39 jackxu-hp ipsec__plutorun: 003 NAT-Traversal: Trying new style NAT-T
Nov 14 12:58:39 jackxu-hp ipsec__plutorun: 003 NAT-Traversal: ESPINUDP(1) setup failed for new style NAT-T family IPv4 (errno=19)
Nov 14 12:58:39 jackxu-hp ipsec__plutorun: 003 NAT-Traversal: Trying old style NAT-T
104 "CUHKVPN" #1: STATE_MAIN_I1: initiate
003 "CUHKVPN" #1: received Vendor ID payload [RFC 3947] method set to=109
106 "CUHKVPN" #1: STATE_MAIN_I2: sent MI2, expecting MR2
003 "CUHKVPN" #1: received Vendor ID payload [Cisco-Unity]
003 "CUHKVPN" #1: received Vendor ID payload [Dead Peer Detection]
003 "CUHKVPN" #1: ignoring unknown Vendor ID payload [7217250aaec6ffe38be2c1b455ff011a]
003 "CUHKVPN" #1: received Vendor ID payload [XAUTH]
003 "CUHKVPN" #1: NAT-Traversal: Result using RFC 3947 (NAT-Traversal): no NAT detected
108 "CUHKVPN" #1: STATE_MAIN_I3: sent MI3, expecting MR3
004 "CUHKVPN" #1: STATE_MAIN_I4: ISAKMP SA established {auth=OAKLEY_PRESHARED_KEY cipher=oakley_3des_cbc_192 prf=oakley_sha group=modp1024}
117 "CUHKVPN" #2: STATE_QUICK_I1: initiate
003 "CUHKVPN" #2: ignoring informational payload, type IPSEC_RESPONDER_LIFETIME msgid=652850f0
004 "CUHKVPN" #2: STATE_QUICK_I2: sent QI2, IPsec SA established transport mode {ESP=>0x27475bb2 <0x7ef71366 xfrm=AES_128-HMAC_SHA1 NATOA=none NATD=none DPD=none}
xl2tpd[3731]: Connecting to host vpn.cuhk.edu.hk, port 1701
xl2tpd[3731]: handle_avps: don't know how to handle atribute 110.
xl2tpd[3731]: handle_avps: don't know how to handle atribute 111.
xl2tpd[3731]: Connection established to 137.189.192.201, 1701. Local: 54648, Remote: 32313 (ref=0/0).
xl2tpd[3731]: Calling on tunnel 54648
xl2tpd[3731]: Call established with 137.189.192.201, Local: 59092, Remote: 63952, Serial: 1 (ref=0/0)
xl2tpd[3731]: start_pppd: I'm running:
xl2tpd[3731]: "/usr/sbin/pppd"
xl2tpd[3731]: "passive"
xl2tpd[3731]: "nodetach"
xl2tpd[3731]: ":"
xl2tpd[3731]: "file"
xl2tpd[3731]: "/etc/ppp/CUHKVPN.options.xl2tpd"
xl2tpd[3731]: "ipparam"
xl2tpd[3731]: "137.189.192.201"
xl2tpd[3731]: "/dev/pts/0"
pppd[3782]: Plugin passprompt.so loaded.
pppd[3782]: pppd 2.4.5 started by root, uid 0
pppd[3782]: Using interface ppp0
pppd[3782]: Connect: ppp0 <--> /dev/pts/0
pppd[3782]: No response to PAP authenticate-requests
pppd[3782]: Connection terminated.
pppd[3782]: Exit.xl2tpd[3731]: control_finish: Connection closed to 137.189.192.201, port 1701 (No application/session timer expired), Local: 54648, Remote: 32313
xl2tpd[3731]: Terminating pppd: sending TERM signal to pid 3782

xl2tpd[3731]: child_handler : pppd exited for call 63952 with code 19
xl2tpd[3731]: call_close: Call 59092 to 137.189.192.201 disconnected

===============================================(End of log)

Any suggestions are welcomed.

Thanks.