I'm getting the following error in roundcube 0.7.2:
Class 'rcube' not found in ~/plugins/globaladdressbook/globaladdressbook.php on line 24
hi. you have downloaded the wrong version of the plugin. please use the version tagged for 0.7.2. the master branch version requires the latest rc svn trunk version of the core.
I changed the plugin rcube to rcmail and the plug-in works fine.