On November 17, 2014, the Google Calendar API v2 was deprecated. This module, and others on drupal.org, depended on and used that API. The 7.x-2.x branch of Agenda was created to convert the module to use Google Calendar API v3. The 6.x-2.x branch was then also created and made the same changes (see #2376795. See the README for installation instructions when updating. Use with caution in production environments.