Many thanks Glitch
Ok, I reinstalled the clean firmware WITHOUT reserving the settings. Now no more authentication problems :-))
However I cannot connect with WAN cable, When i click on interface/connect, it tries, but cannot connect. I even tried to change cable. When I plug the same cable into my old router (also with openWRT) it works and I get internet access.
So I wonder what may be the problem since I just made a clean reinstall and touched nothing, just default settings.
This is the system log https://pastebin.com/z4QU0GyA