[strongSwan] How to troubleshoot error of ENCAPSULATION_MODE_UDP_TRANSPORT_RFC must only be used if NAT-Traversal is detected

[Rv Rv]

Hello everyone
I am newbie to strongswan. I set up kubuntu using http://samsclass.info/ipv6/proj/proj-L5-VPN-Server.html

and get the following error when trying connect to strongswan VPN through iOS. With windows it works through. I searched in the strongswan mailing list and elsewhere but coulf not find anything to rectify this.  Here is the difference that I found in the logs

With iOS it says

	1. "L2TP-PSK-NAT"[2] 192.168.10.6 #53: the peer proposed:
192.168.10.8/32:17/1701 -> 192.168.10.6/32:17/58706

	2.  "L2TP-PSK-NAT"[36] 192.168.10.6 #54:
ENCAPSULATION_MODE_UDP_TRANSPORT_RFC must only be used if NAT-Traversal is detected

	3.  "L2TP-PSK-NAT"[36] 192.168.10.6 #54: sending encrypted notification
BAD_PROPOSAL_SYNTAX to 192.168.10.6:4500

	4. "L2TP-PSK-NAT"[36] 192.168.10.6: deleting connection
"L2TP-PSK-NAT" instance with peer 192.168.10.6 {isakmp=#0/ipsec=#0}

With windows, it says
	1. "L2TP-PSK-NAT"[35] 192.168.10.20 #51: the peer proposed:
192.168.10.8/32:17/1701 -> 192.168.10.20/32:17/0

	2. "L2TP-PSK-NAT"[35] 192.168.10.20 #52: responding to Quick Mode
proposal {msgid:34008be2}

Any inputs appreciated
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.strongswan.org/pipermail/users/attachments/20130703/e7716150/attachment.html>