I get the following error after I upgraded to 2.0. Cannot seem to solve the problem.
Warning: htmlspecialchars(): Invalid multibyte sequence in argument in /var/www/html/piwik/vendor/twig/twig/lib/Twig/Extension/Core.php on line 968
Backtrace -->
#0 Piwik\Error::errorHandler(…) called at [:]
#1 htmlspecialchars(…) called at [/var/www/html/piwik/vendor/twig/twig/lib/Twig/Extension/Core.php:968]
#2 twig_escape_filter(…) called at [/var/www/html/piwik/tmp/templates_c/4d/59/fd5ab243ed2b4c6abc6ef31c7d31ae9e45bdff60578d2627e7e40e242c8d.php:278]
#3 __TwigTemplate_4d59fd5ab243ed2b4c6abc6ef31c7d31ae9e45bdff60578d2627e7e40e242c8d->doDisplay(…) called at [/var/www/html/piwik/vendor/twig/twig/lib/Twig/Template.php:276]
#4 Twig_Template->displayWithErrorHandling(…) called at [/var/www/html/piwik/vendor/twig/twig/lib/Twig/Template.php:250]
#5 Twig_Template->display(…) called at [/var/www/html/piwik/tmp/templates_c/87/30/55a70a99412a2c36f4a4f63c2fa07e58b1a192bc2d9c624d5f484c423e91.php:117]
#6 __TwigTemplate_873055a70a99412a2c36f4a4f63c2fa07e58b1a192bc2d9c624d5f484c423e91->doDisplay(…) called at [/var/www/html/piwik/vendor/twig/twig/lib/Twig/Template.php:276]
#7 Twig_Template->displayWithErrorHandling(…) called at [/var/www/html/piwik/vendor/twig/twig/lib/Twig/Template.php:250]
#8 Twig_Template->display(…) called at [/var/www/html/piwik/vendor/twig/twig/lib/Twig/Template.php:261]
#9 Twig_Template->render(…) called at [/var/www/html/piwik/vendor/twig/twig/lib/Twig/Environment.php:292]
#10 Twig_Environment->render(…) called at [/var/www/html/piwik/core/View.php:253]
#11 Piwik\View->renderTwigTemplate(…) called at [/var/www/html/piwik/core/View.php:248]
#12 Piwik\View->render(…) called at [/var/www/html/piwik/core/Plugin/ViewDataTable.php:363]
#13 Piwik\Plugin\ViewDataTable->render(…) called at [/var/www/html/piwik/core/Plugin/Controller.php:230]
#14 Piwik\Plugin\Controller->renderReport(…) called at [/var/www/html/piwik/plugins/Live/Controller.php:96]
#15 Piwik\Plugins\Live\Controller->getLastVisitsDetails(…) called at [/var/www/html/piwik/plugins/Live/Controller.php:90]
#16 Piwik\Plugins\Live\Controller->indexVisitorLog(…) called at [:]
#17 call_user_func_array(…) called at [/var/www/html/piwik/core/FrontController.php:117]
#18 Piwik\FrontController->dispatch(…) called at [/var/www/html/piwik/index.php:71]