I just tried to upgrade from 1.4 to 1.5-rc7 and I hit the following bug.
I kept getting this error in my apache log (and I’d get a white screen of death with the same message)
PHP Fatal error: Class 'Piwik_Goals' not found in /var/www/piwik/plugins/Goals/API.php on line 300
I don’t use the Goals plugin so it was disabled. However for some reason a code path was running that assumed it was. I commented out line 300 in API.php and Piwik sprang into life. Once done, I enabled the Goals plugin and then uncommented the commented out line.
Piwik is now working properly.
This should be checked for users, like me, that aren’t using the goals plugin and will stumble when they hit this error.