We've been building web sites for years using the Open Source Drupal Content Management System. This site is being built with version 4.7 of this modular and extensible CMS framework.
Every once in a while, a software framework goes through a significant update that makes things better for the future while throwing a compatability curve to the past. There are dozens and dozens of Drupal modules – pluggable code-sets that add useful functionality to the base system – that have evolved over the years of Drupal's development. The 4.7 release introduced some much-needed enhancements to the core functionality of Drupal. These changes meant most modules need to be updated for compatability.