We recommend to upgrade ASAP to the latest Joomla and AutoTweetNG stable versions.
Not only Joomla is upgrading, Facebook, Twitter, and LinkedIn have updated their APIs.
1st-movers.com, the original author site is not longer in the air, and the old versions can't authorize directly the channels.
To make the old version work:
1. Install AutoTweetNG v4.12 or AutoTweetNG v5.10 in your site.
2. Create a testing site with Joomla 2.5, install and configure AutoTweetNG latest version (right now v6.3.3). (Check the online tutorial)
3. Copy the Authorization Tokens to the previous AutoTweetNG version.
In any case, please visit the documentation area or post a ticket.