Error after update v2.5.0 Undefined index: enabled in /var/www/clients/client1/web2/web/analytics/core/Development.php

After updating the piwik system to v2.5.0 the following error occurred and i have not been able to fix it as of yet. Any ideas?

Notice: Undefined index: enabled in /var/www/clients/client1/web2/web/analytics/core/Development.php on line 34

Backtrace -->

#0 Piwik\Error::errorHandler(…) called at [/var/www/clients/client1/web2/web/analytics/core/Development.php:34]
#1 Piwik\Development::isEnabled(…) called at [/var/www/clients/client1/web2/web/analytics/core/Cache/PersistentCache.php:94]
#2 Piwik\Cache\PersistentCache::populateCache(…) called at [/var/www/clients/client1/web2/web/analytics/core/Cache/PersistentCache.php:49]
#3 Piwik\Cache\PersistentCache->__construct(…) called at [/var/www/clients/client1/web2/web/analytics/core/Plugin.php:141]
#4 Piwik\Plugin->__construct(…) called at [/var/www/clients/client1/web2/web/analytics/core/Plugin/Manager.php:870]
#5 Piwik\Plugin\Manager->makePluginClass(…) called at [/var/www/clients/client1/web2/web/analytics/core/Plugin/Manager.php:836]
#6 Piwik\Plugin\Manager->loadPlugin(…) called at [/var/www/clients/client1/web2/web/analytics/core/Plugin/Manager.php:776]
#7 Piwik\Plugin\Manager->reloadPlugins(…) called at [/var/www/clients/client1/web2/web/analytics/core/Plugin/Manager.php:615]
#8 Piwik\Plugin\Manager->loadPlugins(…) called at [/var/www/clients/client1/web2/web/analytics/core/Plugin/Manager.php:95]
#9 Piwik\Plugin\Manager->loadActivatedPlugins(…) called at [/var/www/clients/client1/web2/web/analytics/core/FrontController.php:323]
#10 Piwik\FrontController->init(…) called at [/var/www/clients/client1/web2/web/analytics/core/dispatch.php:33]
#11 require_once(…) called at [/var/www/clients/client1/web2/web/analytics/index.php:47]

A fatal error occurred

The following error just broke Piwik (v2.5.0):

Undefined class constant 'Piwik\Tracker\GoalManager::TYPE_BUYER_NONE’
in
/var/www/clients/client1/web2/web/analytics/core/Singleton.php line 37

I had a similar error after a manual upgrade. In my case, the solution was quite simple: I had not copied the directory config onto my FTP server, fearing to lose my configurations. After uploading this folder, Piwik could be upgraded via the web browser and works.

Overwrite the config/global.ini.php by the latest global.ini.php from the Piwik package.