Comment 39 for bug 256054

Same problem here (Kubuntu Intrepid), though I found a different solution: I commented out the "iface XXX inet dhcp"-lines and now NM works like a charm again.

Here's my /etc/network/interfaces, just to make it clear, what I mean:

# This file describes the network interfaces available on your system
# and how to activate them. For more information, see interfaces(5).

# The loopback network interface
auto lo
iface lo inet loopback

# The primary network interface
auto eth0
#iface eth0 inet dhcp

# The wireless network interface
auto wlan0
#iface wlan0 inet dhcp