I upgraded my Lucid from beta 2 to RC. I deleted all things of beta 2 (I am using this in my virtual machine environment) and installed RC from scratch. In this condition, I tried gwibber as the first starting application, but this still occurred.

ubuntu-rc:~> dpkg -s gwibber
Package: gwibber
Status: install ok installed
Priority: optional
Section: misc
Installed-Size: 2640
Maintainer: Ubuntu Developers <--------------@lists.ubuntu.com>
Architecture: all
Version: 2.30.0.1-0ubuntu1
Depends: python-dbus, python-gtk2, python-gconf, python-egenix-mxdatetime, python-simplejson, python-webkit, librsvg2-2, librsvg2-common, python-imaging, python-xdg, python-mako, python-gtkspell, python-wnck, python-desktopcouch-records, gwibber-service (= 2.30.0.1-0ubuntu1), python (>= 2.6), python-central (>= 0.6.11)
Suggests: gwibber-themes
Conffiles:
 /etc/xdg/autostart/gwibber.desktop ---------------------------------------
Description: Open source social networking client for GNOME
 Gwibber is a social networking client for GNOME. It supports Facebook,
 Twitter, Identi.ca, StatusNet, FriendFeed, Qaiku, Flickr, and Digg.
 .
 This package includes the Gwibber desktop client
Homepage: https://launchpad.net/gwibber
Python-Version: >=2.6

== from ~/.cache/gwibber/gwibber.log
2010-04-27 09:28:10,535 - Gwibber GNOME Client - INFO - Running from the system path
2010-04-27 09:28:28,303 - Gwibber Service - INFO - Running from the system path
2010-04-27 09:28:29,893 - Gwibber Dispatcher - INFO - Gwibber Service is reloading account credentials
2010-04-27 09:28:30,875 - Gwibber Accounts - INFO - Running from the system path
2010-04-27 09:28:44,248 - Gwibber Dispatcher - INFO - Gwibber Service is reloading account credentials
2010-04-27 09:28:52,714 - Gwibber Dispatcher - ERROR - Failed to communicate with https://twitter.com/statuses/mentions.json?count=200
2010-04-27 09:28:52,716 - Gwibber Dispatcher - ERROR - Failed to parse the response, error was: No JSON object could be decoded
2010-04-27 09:28:52,716 - Gwibber Dispatcher - ERROR - <twitter:responses> Operation failed
2010-04-27 09:28:52,724 - Gwibber Dispatcher - ERROR - Failed to communicate with https://twitter.com/statuses/home_timeline.json?count=200
2010-04-27 09:28:52,727 - Gwibber Dispatcher - ERROR - Failed to parse the response, error was: No JSON object could be decoded
2010-04-27 09:28:52,727 - Gwibber Dispatcher - ERROR - <twitter:receive> Operation failed
2010-04-27 09:28:55,812 - Gwibber Dispatcher - ERROR - Failed to communicate with https://twitter.com/statuses/home_timeline.json?count=200
2010-04-27 09:28:55,815 - Gwibber Dispatcher - ERROR - Failed to communicate with https://twitter.com/statuses/mentions.json?count=200
2010-04-27 09:28:55,817 - Gwibber Dispatcher - ERROR - Failed to parse the response, error was: No JSON object could be decoded
2010-04-27 09:28:55,819 - Gwibber Dispatcher - ERROR - Failed to parse the response, error was: No JSON object could be decoded
2010-04-27 09:28:55,819 - Gwibber Dispatcher - ERROR - <twitter:receive> Operation failed
2010-04-27 09:28:55,819 - Gwibber Dispatcher - ERROR - <twitter:responses> Operation failed
2010-04-27 09:29:00,817 - Gwibber Dispatcher - ERROR - Failed to communicate with https://twitter.com/direct_messages.json?count=200
2010-04-27 09:29:00,818 - Gwibber Dispatcher - ERROR - Failed to parse the response, error was: No JSON object could be decoded
2010-04-27 09:29:00,819 - Gwibber Dispatcher - ERROR - <twitter:private> Operation failed
2010-04-27 09:29:00,827 - Gwibber Dispatcher - INFO - Loading complete: 1 - ['Failure', 'Failure', 'Failure']
2010-04-27 09:29:03,962 - Gwibber Dispatcher - ERROR - Failed to communicate with https://twitter.com/direct_messages.json?count=200
2010-04-27 09:29:03,962 - Gwibber Dispatcher - ERROR - Failed to parse the response, error was: No JSON object could be decoded
2010-04-27 09:29:03,963 - Gwibber Dispatcher - ERROR - <twitter:private> Operation failed
2010-04-27 09:29:03,964 - Gwibber Dispatcher - INFO - Loading complete: 2 - ['Failure', 'Failure', 'Failure']

Of course, my Twitter account and password is correct.
I tried to add my account both from gwibber application and "Me environment" (broadcast account) from upper right icon of the desktop. The result were same ... failure for login.