As you suggested I made a fresh format (fat32 as before) of the usb-stick.
Also downloaded the linux version (unetbootin-linux-575) of unetbootin and
run it with Knoppix 6.7.1 as host.http://unetbootin.sourceforge.net/
I pointed it to the downloaded iso-file I used before.
Unetbootin first complained that the usb-stick was not mounted.
That might be done in a terminal window. I however "clicked" the volume icon i the Knoppix file
manager which is sufficient in most linux distributions to accomplish a mount.
When Unetbootin finished I booted on the usb-stick.
It was now possible to access other partitions of my choice and change time settings without a prompt
for a root password or have to be root.
It was also possible to open Accessories - Root terminal without giving password.
And in a Terminal window "sudo su" and the passwd command functioned.
Better use this new won functionality to set a root password.
Probably there is a flaw in the Universal USB Installer. I have encountered problems with the UUI when I tried to
make a hd install from a usb-stick with a UUI creation.
Thanks all of you for your help and concern!