Error backtrace after update to 2.3.0 (3 replies)

Hello,
it is impossible to log in and there seems nothing I can do.
I pasted the backtrace below.
I hope there is a solution!
Thanks a lot!
Thorsten
_____________________________________________________________________________________
There is an error. Please report the message (Piwik 2.3.0) and full backtrace in the Piwik forums (please do a Search first as it might have been reported already!).

Notice: Undefined index: ExternalHelp in /mnt/web1/c2/39/52198939/htdocs/Piwik_02/core/Translate.php on line 161

Backtrace -->

#0 Piwik\Error::errorHandler(...) called at [/mnt/web1/c2/39/52198939/htdocs/Piwik_02/core/Translate.php:161]
#1 Piwik\Translate::getJavascriptTranslations(...) called at [/mnt/web1/c2/39/52198939/htdocs/Piwik_02/core/AssetManager.php:121]
#2 Piwik\AssetManager->getJsInclusionDirective(...) called at [/mnt/web1/c2/39/52198939/htdocs/Piwik_02/core/Twig.php:126]
#3 Piwik\Twig->Piwik\{closure}(...) called at [:]
#4 call_user_func_array(...) called at [/mnt/web1/c2/39/52198939/htdocs/Piwik_02/tmp/templates_c/d9/29/5c8999755c423bd4153701c296d38e9b3cffb5d4586f9e4bd3805765574d.php:24]
#5 __TwigTemplate_d9295c8999755c423bd4153701c296d38e9b3cffb5d4586f9e4bd3805765574d->doDisplay(...) called at [/mnt/web1/c2/39/52198939/htdocs/Piwik_02/vendor/twig/twig/lib/Twig/Template.php:276]
#6 Twig_Template->displayWithErrorHandling(...) called at [/mnt/web1/c2/39/52198939/htdocs/Piwik_02/vendor/twig/twig/lib/Twig/Template.php:250]
#7 Twig_Template->display(...) called at [/mnt/web1/c2/39/52198939/htdocs/Piwik_02/tmp/templates_c/3b/87/4a56d408c2c8a2d659d9552a31ea9d6536f0e7ad357f3a340451cd1f03ab.php:54]
#8 __TwigTemplate_3b874a56d408c2c8a2d659d9552a31ea9d6536f0e7ad357f3a340451cd1f03ab->doDisplay(...) called at [/mnt/web1/c2/39/52198939/htdocs/Piwik_02/vendor/twig/twig/lib/Twig/Template.php:276]
#9 Twig_Template->displayWithErrorHandling(...) called at [/mnt/web1/c2/39/52198939/htdocs/Piwik_02/vendor/twig/twig/lib/Twig/Template.php:250]
#10 Twig_Template->display(...) called at [/mnt/web1/c2/39/52198939/htdocs/Piwik_02/vendor/twig/twig/lib/Twig/Template.php:261]
#11 Twig_Template->render(...) called at [/mnt/web1/c2/39/52198939/htdocs/Piwik_02/vendor/twig/twig/lib/Twig/Environment.php:292]
#12 Twig_Environment->render(...) called at [/mnt/web1/c2/39/52198939/htdocs/Piwik_02/core/View.php:245]
#13 Piwik\View->renderTwigTemplate(...) called at [/mnt/web1/c2/39/52198939/htdocs/Piwik_02/core/View.php:240]
#14 Piwik\View->render(...) called at [/mnt/web1/c2/39/52198939/htdocs/Piwik_02/plugins/Login/Controller.php:99]
#15 Piwik\Plugins\Login\Controller->login(...) called at [/mnt/web1/c2/39/52198939/htdocs/Piwik_02/plugins/Login/Controller.php:61]
#16 Piwik\Plugins\Login\Controller->index(...) called at [:]
#17 call_user_func_array(...) called at [/mnt/web1/c2/39/52198939/htdocs/Piwik_02/core/FrontController.php:500]
#18 Piwik\FrontController->doDispatch(...) called at [/mnt/web1/c2/39/52198939/htdocs/Piwik_02/core/FrontController.php:85]
#19 Piwik\FrontController->dispatch(...) called at [/mnt/web1/c2/39/52198939/htdocs/Piwik_02/index.php:62]