Hi,
"Still when I click on "back up now", it doesn´t work properly. It starts loading, but gets stuck after a while and never finishes."
When you say it gets stuck, at what stage? Please can you paste the complete log? (Use pastebin.com or something similar - it'll be too long for this forum).
Debug messages: Turn of the debugging option in the UpdraftPlus settings if you don't want to see debugging messages printed on your screen.
Best wishes,
David