Dear pavit
Thanks for you help, it works now.
I still get the same compilation error when I have the file "/less/style.less" selected and try to start the compilaton from there. --> So if I got you right I first have to close the file, close the view "Templates Customise (Ja_sugite)", open the "Templates Edit Style" view and can then successfully start the compilation with the buttom "LESS to CSS" (Development Mode = ON).
I then shortly get an error message "Unexpected error. Please refresh the page try again later." That message disappears few seconds later and things work. I can now change the file "style.less" forth and back and compile that way to turn rotation of the logo on and of. So it works. :-)
I have changed the password of the new super user, so don't be surprised if you cannot login anymore. Thanks again!