Cannot log into instance when network_manager=FlatManager

If I set network_manager to FlatManager, I can start a new instance, but cannot log into it.

The result of the euca-run-instances is something like the followings:
{{{
RESERVATION r-sw4pptr7 IRT
INSTANCE i-00000001 ami-qzt0fqao 10.0.0.2 10.0.0.2 running mykey (IRT, ubuntu7) 0 m1.tiny 2011-01-14 08:06:22 nova
}}}

And nova.conf is as followings:
ubuntu7 = 192.168.32.202
{{{
--sql_connection=mysql://root:nova@ubuntu7/nova
--s3_host=ubuntu7
--rabbit_host=192.168.32.202
--cc_host=192.168.32.202
--ec2_url=http://192.168.32.202:8773/services/Cloud

--daemonize=1

--dhcpbridge_flagfile=/etc/nova/nova.conf
--dhcpbridge=/usr/bin/nova-dhcpbridge

--FAKE_subdomain=ec2

--ca_path=/var/lib/nova/CA
--keys_path=/var/lib/nova/keys
--networks_path=/var/lib/nova/networks
--instances_path=/var/lib/nova/instances
--images_path=/var/lib/nova/images
--buckets_path=/var/lib/nova/buckets

--libvirt_type=kvm

--network_manager=nova.network.manager.FlatManager

--vlan_interface=eth0

--logdir=/var/log/nova
--verbose
--volume_group=ubuntu7
--fixed_range=192.168.2.64/26
--network_size=64
}}}

The last part of euca-get-console-output's output is as followings:
{{{
Jan 14 08:08:30 ttylinux_host authpriv.info dropbear[267]: Running in background
############ debug end ##############
cloud-setup: failed to read iid from metadata. tried 30
stty: \/dev\/console
sshd is already running.
stty: \/dev\/console
startup inetd [ OK ]
stty: \/dev\/console
startup crond [ OK ]
wget: can't connect to remote host (169.254.169.254): No route to host
cloud-userdata: failed to read instance id
===== cloud-final: system completely up in 127.97 seconds ====
wget: can't connect to remote host (169.254.169.254): No route to host
wget: can't connect to remote host (169.254.169.254): No route to host
wget: can't connect to remote host (169.254.169.254): No route to host
  instance-id:
  public-ipv4:
  local-ipv4 :
=> First-Boot Sequence:
setting shared object cache [running ldconfig] [ OK ]
}}}

And /etc/network/interfaces is as followings:
{{{
auto lo
iface lo inet loopback

auto br100
iface br100 inet dhcp
          bridge_ports eth0
          bridge_stp off
          bridge_maxwait 0
          bridge_fd 0
}}}

Does anybody has some ideas about this problem?