Registration - Thank you page Error - Call to undefined method -Joomla
At administer - system settings - directories, there's one called custom php path that contains a folder path. Go look in that path in the filesystem and you probably have a customized version of CRM/Core/BAO/UFGroup.php. It will need to be updated with some recent changes that were made to the real CRM/Core/BAO/UFGroup.php, in particular the addition of the function getFrontEndTitle().