I installed a MAAS server into a VM w/ the beta2 quantal cd:
  ubuntu-12.10-beta2-server-amd64.iso

I did pass console=ttyS0, and I am in an environment w/ no NTP server, but other than that a very "vanilla" install. After the intall completed, browsing to the UI page gave me an HTTP 200 error. I dug through the apache logs, and found messages like this whenever I'd hit refresh on the UI page:

==> error.log <==
[Thu Oct 11 18:03:33 2012] [error] [client 10.250.35.107] mod_wsgi (pid=1173): Target WSGI script '/usr/share/maas/wsgi.py' cannot be loaded as Python module.
[Thu Oct 11 18:03:33 2012] [error] [client 10.250.35.107] mod_wsgi (pid=1173): Exception occurred processing WSGI script '/usr/share/maas/wsgi.py'.
[Thu Oct 11 18:03:33 2012] [error] [client 10.250.35.107] Traceback (most recent call last):
[Thu Oct 11 18:03:33 2012] [error] [client 10.250.35.107]   File "/usr/share/maas/wsgi.py", line 30, in <module>
[Thu Oct 11 18:03:33 2012] [error] [client 10.250.35.107]     start_up()
[Thu Oct 11 18:03:33 2012] [error] [client 10.250.35.107]   File "/usr/lib/python2.7/dist-packages/maasserver/start_up.py", line 59, in start_up
[Thu Oct 11 18:03:33 2012] [error] [client 10.250.35.107]     inner_start_up()
[Thu Oct 11 18:03:33 2012] [error] [client 10.250.35.107]   File "/usr/lib/python2.7/dist-packages/maasserver/start_up.py", line 87, in inner_start_up
[Thu Oct 11 18:03:33 2012] [error] [client 10.250.35.107]     write_full_dns_config(reload_retry=True)
[Thu Oct 11 18:03:33 2012] [error] [client 10.250.35.107]   File "/usr/lib/python2.7/dist-packages/maasserver/dns.py", line 309, in write_full_dns_config
[Thu Oct 11 18:03:33 2012] [error] [client 10.250.35.107]     args=[['reload'], reload_retry]))
[Thu Oct 11 18:03:33 2012] [error] [client 10.250.35.107]   File "/usr/lib/python2.7/dist-packages/celery/app/task/__init__.py", line 353, in delay
[Thu Oct 11 18:03:33 2012] [error] [client 10.250.35.107]     return self.apply_async(args, kwargs)
[Thu Oct 11 18:03:33 2012] [error] [client 10.250.35.107]   File "/usr/lib/python2.7/dist-packages/celery/app/task/__init__.py", line 449, in apply_async
[Thu Oct 11 18:03:33 2012] [error] [client 10.250.35.107]     publish = publisher or self.app.amqp.publisher_pool.acquire(block=True)
[Thu Oct 11 18:03:33 2012] [error] [client 10.250.35.107]   File "/usr/lib/python2.7/dist-packages/kombu/connection.py", line 657, in acquire
[Thu Oct 11 18:03:33 2012] [error] [client 10.250.35.107]     R = self.prepare(R)
[Thu Oct 11 18:03:33 2012] [error] [client 10.250.35.107]   File "/usr/lib/python2.7/dist-packages/kombu/pools.py", line 54, in prepare
[Thu Oct 11 18:03:33 2012] [error] [client 10.250.35.107]     p = p()
[Thu Oct 11 18:03:33 2012] [error] [client 10.250.35.107]   File "/usr/lib/python2.7/dist-packages/kombu/pools.py", line 45, in <lambda>
[Thu Oct 11 18:03:33 2012] [error] [client 10.250.35.107]     return lambda: self.create_producer()
[Thu Oct 11 18:03:33 2012] [error] [client 10.250.35.107]   File "/usr/lib/python2.7/dist-packages/celery/app/amqp.py", line 265, in create_producer
[Thu Oct 11 18:03:33 2012] [error] [client 10.250.35.107]     pub = self.app.amqp.TaskPublisher(conn, auto_declare=False)
[Thu Oct 11 18:03:33 2012] [error] [client 10.250.35.107]   File "/usr/lib/python2.7/dist-packages/celery/app/amqp.py", line 328, in TaskPublisher
[Thu Oct 11 18:03:33 2012] [error] [client 10.250.35.107]     return TaskPublisher(*args, **self.app.merge(defaults, kwargs))
[Thu Oct 11 18:03:33 2012] [error] [client 10.250.35.107]   File "/usr/lib/python2.7/dist-packages/celery/app/amqp.py", line 158, in __init__
[Thu Oct 11 18:03:33 2012] [error] [client 10.250.35.107]     super(TaskPublisher, self).__init__(*args, **kwargs)
[Thu Oct 11 18:03:33 2012] [error] [client 10.250.35.107]   File "/usr/lib/python2.7/dist-packages/kombu/compat.py", line 61, in __init__
[Thu Oct 11 18:03:33 2012] [error] [client 10.250.35.107]     super(Publisher, self).__init__(connection, self.exchange, **kwargs)
[Thu Oct 11 18:03:33 2012] [error] [client 10.250.35.107]   File "/usr/lib/python2.7/dist-packages/kombu/messaging.py", line 79, in __init__
[Thu Oct 11 18:03:33 2012] [error] [client 10.250.35.107]     self.revive(self.channel)
[Thu Oct 11 18:03:33 2012] [error] [client 10.250.35.107]   File "/usr/lib/python2.7/dist-packages/kombu/messaging.py", line 168, in revive
[Thu Oct 11 18:03:33 2012] [error] [client 10.250.35.107]     channel = channel.default_channel
[Thu Oct 11 18:03:33 2012] [error] [client 10.250.35.107]   File "/usr/lib/python2.7/dist-packages/kombu/connection.py", line 581, in default_channel
[Thu Oct 11 18:03:33 2012] [error] [client 10.250.35.107]     self.connection
[Thu Oct 11 18:03:33 2012] [error] [client 10.250.35.107]   File "/usr/lib/python2.7/dist-packages/kombu/connection.py", line 574, in connection
[Thu Oct 11 18:03:33 2012] [error] [client 10.250.35.107]     self._connection = self._establish_connection()
[Thu Oct 11 18:03:33 2012] [error] [client 10.250.35.107]   File "/usr/lib/python2.7/dist-packages/kombu/connection.py", line 533, in _establish_connection
[Thu Oct 11 18:03:33 2012] [error] [client 10.250.35.107]     conn = self.transport.establish_connection()
[Thu Oct 11 18:03:33 2012] [error] [client 10.250.35.107]   File "/usr/lib/python2.7/dist-packages/kombu/transport/amqplib.py", line 279, in establish_connection
[Thu Oct 11 18:03:33 2012] [error] [client 10.250.35.107]     connect_timeout=conninfo.connect_timeout)
[Thu Oct 11 18:03:33 2012] [error] [client 10.250.35.107]   File "/usr/lib/python2.7/dist-packages/kombu/transport/amqplib.py", line 89, in __init__
[Thu Oct 11 18:03:33 2012] [error] [client 10.250.35.107]     super(Connection, self).__init__(*args, **kwargs)
[Thu Oct 11 18:03:33 2012] [error] [client 10.250.35.107]   File "/usr/lib/python2.7/dist-packages/amqplib/client_0_8/connection.py", line 144, in __init__
[Thu Oct 11 18:03:33 2012] [error] [client 10.250.35.107]     (10, 30), # tune
[Thu Oct 11 18:03:33 2012] [error] [client 10.250.35.107]   File "/usr/lib/python2.7/dist-packages/amqplib/client_0_8/abstract_channel.py", line 95, in wait
[Thu Oct 11 18:03:33 2012] [error] [client 10.250.35.107]     self.channel_id, allowed_methods)
[Thu Oct 11 18:03:33 2012] [error] [client 10.250.35.107]   File "/usr/lib/python2.7/dist-packages/amqplib/client_0_8/connection.py", line 202, in _wait_method
[Thu Oct 11 18:03:33 2012] [error] [client 10.250.35.107]     self.method_reader.read_method()
[Thu Oct 11 18:03:33 2012] [error] [client 10.250.35.107]   File "/usr/lib/python2.7/dist-packages/amqplib/client_0_8/method_framing.py", line 221, in read_method
[Thu Oct 11 18:03:33 2012] [error] [client 10.250.35.107]     raise m
[Thu Oct 11 18:03:33 2012] [error] [client 10.250.35.107] error: [Errno 104] Connection reset by peer

==> access.log <==
10.250.35.107 - - [11/Oct/2012:18:03:30 -0500] "GET /MAAS/ HTTP/1.1" 500 630 "-" "Mozilla/5.0 (X11; Ubuntu; Linux i686; rv:16.0) Gecko/20100101 Firefox/16.0"


==> error.log <==
[Thu Oct 11 18:03:38 2012] [error] [client 127.0.0.1] mod_wsgi (pid=1172): Target WSGI script '/usr/share/maas/wsgi.py' cannot be loaded as Python module.
[Thu Oct 11 18:03:38 2012] [error] [client 127.0.0.1] mod_wsgi (pid=1172): Exception occurred processing WSGI script '/usr/share/maas/wsgi.py'.
[Thu Oct 11 18:03:38 2012] [error] [client 127.0.0.1] Traceback (most recent call last):
[Thu Oct 11 18:03:38 2012] [error] [client 127.0.0.1]   File "/usr/share/maas/wsgi.py", line 30, in <module>
[Thu Oct 11 18:03:38 2012] [error] [client 127.0.0.1]     start_up()
[Thu Oct 11 18:03:38 2012] [error] [client 127.0.0.1]   File "/usr/lib/python2.7/dist-packages/maasserver/start_up.py", line 59, in start_up
[Thu Oct 11 18:03:38 2012] [error] [client 127.0.0.1]     inner_start_up()
[Thu Oct 11 18:03:38 2012] [error] [client 127.0.0.1]   File "/usr/lib/python2.7/dist-packages/maasserver/start_up.py", line 87, in inner_start_up
[Thu Oct 11 18:03:38 2012] [error] [client 127.0.0.1]     write_full_dns_config(reload_retry=True)
[Thu Oct 11 18:03:38 2012] [error] [client 127.0.0.1]   File "/usr/lib/python2.7/dist-packages/maasserver/dns.py", line 309, in write_full_dns_config
[Thu Oct 11 18:03:38 2012] [error] [client 127.0.0.1]     args=[['reload'], reload_retry]))
[Thu Oct 11 18:03:38 2012] [error] [client 127.0.0.1]   File "/usr/lib/python2.7/dist-packages/celery/app/task/__init__.py", line 353, in delay
[Thu Oct 11 18:03:38 2012] [error] [client 127.0.0.1]     return self.apply_async(args, kwargs)
[Thu Oct 11 18:03:38 2012] [error] [client 127.0.0.1]   File "/usr/lib/python2.7/dist-packages/celery/app/task/__init__.py", line 449, in apply_async
[Thu Oct 11 18:03:38 2012] [error] [client 127.0.0.1]     publish = publisher or self.app.amqp.publisher_pool.acquire(block=True)
[Thu Oct 11 18:03:38 2012] [error] [client 127.0.0.1]   File "/usr/lib/python2.7/dist-packages/kombu/connection.py", line 657, in acquire
[Thu Oct 11 18:03:38 2012] [error] [client 127.0.0.1]     R = self.prepare(R)
[Thu Oct 11 18:03:38 2012] [error] [client 127.0.0.1]   File "/usr/lib/python2.7/dist-packages/kombu/pools.py", line 54, in prepare
[Thu Oct 11 18:03:38 2012] [error] [client 127.0.0.1]     p = p()
[Thu Oct 11 18:03:38 2012] [error] [client 127.0.0.1]   File "/usr/lib/python2.7/dist-packages/kombu/pools.py", line 45, in <lambda>
[Thu Oct 11 18:03:38 2012] [error] [client 127.0.0.1]     return lambda: self.create_producer()
[Thu Oct 11 18:03:38 2012] [error] [client 127.0.0.1]   File "/usr/lib/python2.7/dist-packages/celery/app/amqp.py", line 265, in create_producer
[Thu Oct 11 18:03:38 2012] [error] [client 127.0.0.1]     pub = self.app.amqp.TaskPublisher(conn, auto_declare=False)
[Thu Oct 11 18:03:38 2012] [error] [client 127.0.0.1]   File "/usr/lib/python2.7/dist-packages/celery/app/amqp.py", line 328, in TaskPublisher
[Thu Oct 11 18:03:38 2012] [error] [client 127.0.0.1]     return TaskPublisher(*args, **self.app.merge(defaults, kwargs))
[Thu Oct 11 18:03:38 2012] [error] [client 127.0.0.1]   File "/usr/lib/python2.7/dist-packages/celery/app/amqp.py", line 158, in __init__
[Thu Oct 11 18:03:38 2012] [error] [client 127.0.0.1]     super(TaskPublisher, self).__init__(*args, **kwargs)
[Thu Oct 11 18:03:38 2012] [error] [client 127.0.0.1]   File "/usr/lib/python2.7/dist-packages/kombu/compat.py", line 61, in __init__
[Thu Oct 11 18:03:38 2012] [error] [client 127.0.0.1]     super(Publisher, self).__init__(connection, self.exchange, **kwargs)
[Thu Oct 11 18:03:38 2012] [error] [client 127.0.0.1]   File "/usr/lib/python2.7/dist-packages/kombu/messaging.py", line 79, in __init__
[Thu Oct 11 18:03:38 2012] [error] [client 127.0.0.1]     self.revive(self.channel)
[Thu Oct 11 18:03:38 2012] [error] [client 127.0.0.1]   File "/usr/lib/python2.7/dist-packages/kombu/messaging.py", line 168, in revive
[Thu Oct 11 18:03:38 2012] [error] [client 127.0.0.1]     channel = channel.default_channel
[Thu Oct 11 18:03:38 2012] [error] [client 127.0.0.1]   File "/usr/lib/python2.7/dist-packages/kombu/connection.py", line 581, in default_channel
[Thu Oct 11 18:03:38 2012] [error] [client 127.0.0.1]     self.connection
[Thu Oct 11 18:03:38 2012] [error] [client 127.0.0.1]   File "/usr/lib/python2.7/dist-packages/kombu/connection.py", line 574, in connection
[Thu Oct 11 18:03:38 2012] [error] [client 127.0.0.1]     self._connection = self._establish_connection()
[Thu Oct 11 18:03:38 2012] [error] [client 127.0.0.1]   File "/usr/lib/python2.7/dist-packages/kombu/connection.py", line 533, in _establish_connection
[Thu Oct 11 18:03:38 2012] [error] [client 127.0.0.1]     conn = self.transport.establish_connection()
[Thu Oct 11 18:03:38 2012] [error] [client 127.0.0.1]   File "/usr/lib/python2.7/dist-packages/kombu/transport/amqplib.py", line 279, in establish_connection
[Thu Oct 11 18:03:38 2012] [error] [client 127.0.0.1]     connect_timeout=conninfo.connect_timeout)
[Thu Oct 11 18:03:38 2012] [error] [client 127.0.0.1]   File "/usr/lib/python2.7/dist-packages/kombu/transport/amqplib.py", line 89, in __init__
[Thu Oct 11 18:03:38 2012] [error] [client 127.0.0.1]     super(Connection, self).__init__(*args, **kwargs)
[Thu Oct 11 18:03:38 2012] [error] [client 127.0.0.1]   File "/usr/lib/python2.7/dist-packages/amqplib/client_0_8/connection.py", line 144, in __init__
[Thu Oct 11 18:03:38 2012] [error] [client 127.0.0.1]     (10, 30), # tune
[Thu Oct 11 18:03:38 2012] [error] [client 127.0.0.1]   File "/usr/lib/python2.7/dist-packages/amqplib/client_0_8/abstract_channel.py", line 95, in wait
[Thu Oct 11 18:03:38 2012] [error] [client 127.0.0.1]     self.channel_id, allowed_methods)
[Thu Oct 11 18:03:38 2012] [error] [client 127.0.0.1]   File "/usr/lib/python2.7/dist-packages/amqplib/client_0_8/connection.py", line 202, in _wait_method
[Thu Oct 11 18:03:38 2012] [error] [client 127.0.0.1]     self.method_reader.read_method()
[Thu Oct 11 18:03:38 2012] [error] [client 127.0.0.1]   File "/usr/lib/python2.7/dist-packages/amqplib/client_0_8/method_framing.py", line 221, in read_method
[Thu Oct 11 18:03:38 2012] [error] [client 127.0.0.1]     raise m
[Thu Oct 11 18:03:38 2012] [error] [client 127.0.0.1] error: [Errno 104] Connection reset by peer

==> access.log <==
127.0.0.1 - - [11/Oct/2012:18:03:35 -0500] "POST /MAAS/api/1.0/nodegroups/?op=register HTTP/1.1" 500 797 "-" "Python-urllib/2.7"


Looking at other logs that appeared at the same time, I see this in RabbiqMQ's log:
=ERROR REPORT==== 11-Oct-2012::18:12:39 ===
closing AMQP connection <0.561.0> (10.35.11.4:36784 -> 10.35.11.4:5672):
{channel0_error,starting,
                {amqp_error,access_refused,
                            "AMQPLAIN login refused: user 'maas_workers' - invalid credentials",
                            'connection.start_ok'}}


'dpkg-reconfigure maas-region-controller' (w/o changing any settings) seems to fix this up.

I was able to reproduce this twice, each with a fresh install from the CD. rbasak attempted to reproduce w/ a clean quantal install + apt-get install maas juju, but that did not demonstrate the problem.