Comment 24 for bug 105251

Network-manager calls dhclient with -sf option set to /usr/lib/NetworkManager/nm-dhcp-client.action which means dhclient doesn't run the traditional dhclient-script upon acquiring the Lease.

$ sudo /sbin/dhclient -d -sf /usr/lib/NetworkManager/nm-dhcp-client.action -pf /var/run/dhclient-eth0.pid -lf /var/run/dhclient-eth0.lease -cf /var/run/nm-dhclient-eth0.conf eth0
Internet Systems Consortium DHCP Client V3.1.1
Copyright 2004-2008 Internet Systems Consortium.
All rights reserved.
For info, please visit http://www.isc.org/sw/dhcp/

wifi0: unknown hardware address type 801
Error: Could not acquire the NM DHCP client service. Message: (org.freedesktop.DBus.Error.AccessDenied) Connection ":1.36" is not allowed to own the service "org.freedesktop.nm_dhcp_client" due to security policies in the configuration file

It seems that NM's own program fails to notify via DBus the acquisition of the Lease. Now, if you add NM's PPA source to your apt list:

deb http://ppa.launchpad.net/network-manager/ubuntu intrepid main

an upgrade from there to version 0.7-0ubuntu1~nm1~intrepid1 then this problem is solved.

To recap the solution, install NetworkManager from the PPA repository and it will solve the problem