After upgrading to 2.3.0 and installing module newsletter-0.1 SilverStripe is working but Newsletter not. in PHP-Errors:
PHP Fatal error: Class 'ProgressBar' not found in /home/silvers/wirt/site/newsletter/code/NewsletterAdmin.php on line 448
After commenting out references to the missing ProgressBar it starts - but is not usable at all. No respond for creating a new mail.
I also have:
PHP Notice: LeftAndMain::add_menu_item is deprecated; use CMSMenu::add_menu_item in /opt/silverstripe-2.3.0-1/cms/code/LeftAndMain.php on line 357
in my error logs.