Dear Rodrigo, thank you for your answer and explanation. The lessons are now working and I can see that Amazon S3 had problems since I wasn't even able to download the Assets!

Hello Pierluigi, have you continued experiencing issues watching this lesson? On our side, the lesson appears to be playing right now. Apparently, there were some errors popping up in Amazon S3, which is our hosting provider for streaming our lessons. Service should be restored pretty soon, apologies for the inconveniences. You can read more about this here: https://thenextweb.com/insider/2017/02/28/amazon-web-services-issue-breaking-entire-internet/#.tnw_hmLDNK5g