May somebody can help me please. Thx
Actually the Server is with a Hosting Provider in Germany ( Stratos) and it looks like the Server keeps closing the connection....
This is a server problem, please contact server support and tell them that you get error message trying to install ufw.
For a masternode VPS, you don't even need UFW. As long as nothing else is running, there is no need to block ports.
apt-get update
apt-get upgrade
apt-get dist-upgrade
that's all that should be needed before you follow the very nicely done MN documentation.
Don't forget sentinel though.
Fusion