thank you for the fast reply.
I thought, I would have done a system upgrade with running the programm "Sparky first run". But it seems so, that it has not functioned.
The 'lxpolkit'-package? Unfortunately I don't know, how I can check this... (I'm a poor MS-Windows-rat)
in the Menu of the Sparky-Desktop I could not discover it...
So I have ignored this point.
I opened the LXTerminal:
The command "remsu sparky-aptus"
had no reaction.
The command "sudo sparky-aptus"
had started the APTus-Programm.
Here I could create an update-list and then run a system-update. The programm downloaded 574MB! and it seemed that the update-process was running.
After this was finished, I started the computer anew.
But unfortunately the problem is the same: I can't start the APTus from the Menu: It seems that it was opening a window in the background for a second, but in the end it doesn't appear a programm-window.
So I repeat the process with opening the LXTerminal and the command "sudo sparky-aptus". Now the programm doesn't create a new update-list; I think because it's done by the first time and I conclude, that the system is now up to date.
At this moment where I write these sentences, I want start the APTus-Programm via opening the LXTerminal and the command "sudo sparky-aptus" again for a better explanation, but the system answers:
"yad: cannot create shared memory for key 123450: Die Datei existiert bereits" ("Die Datei existiert bereits" = "the file already exists")
I think I must start the computer anew.