I had a problem during upgrade from 1.2.0 to 1.2.1 :
Notice: Undefined property: Piwik_CoreUpdater_Controller::$pathRootExtractedPiwik in /var/www/virtual/spheerys.fr/piwik/htdocs/plugins/CoreUpdater/Controller.php on line 99
Backtrace -->
#0 Piwik_ErrorHandler(8, Undefined property: Piwik_CoreUpdater_Controller::$pathRootExtractedPiwik, /var/www/virtual/spheerys.fr/piwik/htdocs/plugins/CoreUpdater/Controller.php, 99, Array ()) called at [/var/www/virtual/spheerys.fr/piwik/htdocs/plugins/CoreUpdater/Controller.php:99]#1 Piwik_CoreUpdater_Controller->oneClick_Unpack() called at [/var/www/virtual/spheerys.fr/piwik/htdocs/plugins/CoreUpdater/Controller.php:63]#2 Piwik_CoreUpdater_Controller->oneClickUpdate()#3 call_user_func_array(Array ([0] => Piwik_CoreUpdater_Controller Object ([] => ,[] => Array (),[] => Array (),[] => Array (),[] => CoreUpdater,[] => ,[] => ,[] => 0,[] => Piwik_Site Object ([] => 0),[newVersion] => 1.2.1,[pathPiwikZip] => /var/www/virtual/spheerys.fr/piwik/htdocs/tmp/latest/latest.zip),[1] => oneClickUpdate), Array ()) called at [/var/www/virtual/spheerys.fr/piwik/htdocs/core/FrontController.php:125]#4 Piwik_FrontController->dispatch() called at [/var/www/virtual/spheerys.fr/piwik/htdocs/index.php:57]