Hi, I got this error message :

Notice: Undefined index: log_writers in /home/www/piwik/core/Log.php on line 272

Warning: array_map(): Argument #2 should be an array in /home/www/piwik/core/Log.php on line 274

Warning: Invalid argument supplied for foreach() in /home/www/piwik/core/Log.php on line 275
There is an error. Please report the message (Piwik 2.0.2) and full backtrace in the Piwik forums (please do a Search first as it might have been reported already!).

Notice: Undefined index: log_writers in /home/www/piwik/core/Log.php on line 272

Backtrace -->
#0 Piwik\Error::errorHandler(...) called at [/home/www/piwik/core/Log.php:272]
#1 Piwik\Log->setLogWritersFromConfig(...) called at [/home/www/piwik/core/Log.php:174]
#2 Piwik\Log->__construct(...) called at [/home/www/piwik/core/Singleton.php:40]
#3 Piwik\Singleton::getInstance(...) called at [/home/www/piwik/core/Log.php:542]
#4 Piwik\Log::logMessage(...) called at [/home/www/piwik/core/Log.php:240]
#5 Piwik\Log::verbose(...) called at [/home/www/piwik/core/ArchiveProcessor/Parameters.php:188]
#6 Piwik\ArchiveProcessor\Parameters->logStatusDebug(...) called at [/home/www/piwik/core/ArchiveProcessor/PluginsArchiver.php:105]
#7 Piwik\ArchiveProcessor\PluginsArchiver->finalizeArchive(...) called at [/home/www/piwik/core/ArchiveProcessor/Loader.php:122]
#8 Piwik\ArchiveProcessor\Loader->prepareAllPluginsArchive(...) called at [/home/www/piwik/core/ArchiveProcessor/Loader.php:74]
#9 Piwik\ArchiveProcessor\Loader->prepareArchive(...) called at [/home/www/piwik/core/Archive.php:793]
#10 Piwik\Archive->prepareArchive(...) called at [/home/www/piwik/core/Archive.php:612]
#11 Piwik\Archive->cacheArchiveIdsAfterLaunching(...) called at [/home/www/piwik/core/Archive.php:554]
#12 Piwik\Archive->getArchiveIds(...) called at [/home/www/piwik/core/Archive.php:494]
#13 Piwik\Archive->get(...) called at [/home/www/piwik/core/Archive.php:343]
#14 Piwik\Archive->getDataTableFromNumeric(...) called at [/home/www/piwik/plugins/MultiSites/API.php:207]
#15 Piwik\Plugins\MultiSites\API->buildDataTable(...) called at [/home/www/piwik/plugins/MultiSites/API.php:107]
#16 Piwik\Plugins\MultiSites\API->getAll(...) called at [/home/www/piwik/plugins/MultiSites/Controller.php:74]
#17 Piwik\Plugins\MultiSites\Controller->getSitesInfo(...) called at [/home/www/piwik/plugins/MultiSites/Controller.php:47]
#18 Piwik\Plugins\MultiSites\Controller->index(...) called at [:]
#19 call_user_func_array(...) called at [/home/www/piwik/core/FrontController.php:117]
#20 Piwik\FrontController->dispatch(...) called at [/home/www/piwik/index.php:71]

I temporarily fixed it by replacing

// set the log writers
        $logWriters = $logConfig[self::LOG_WRITERS_CONFIG_OPTION];```

with

// set the log writers
$logConfig['log_writers'] = array('screen');
$logWriters = $logConfig[self::LOG_WRITERS_CONFIG_OPTION];```

in file : core/Log.php
It seems $logConfig['log_writers'] is not set anywhere

Chag