Hallo! my dear predecessors,
without any intent I must have changed my KWallet password. After more than one year with vexatious nessessitations today I found LinuxQuestions.org, and via the FAQs the problem immediately was solved.

Although the "rules" require posting in English - to my astonishment I found FAQs in German !? Perhaps there is a philanthropist who enlightens me about that little problem.

Welcome to LQ!

great!
since linux forums are a 2-way-street, it would be nice of you to share your solution so that others can benefit from your post.

astonishing indeed.
could you point us to one such page? have not found anything here.

My first visit to LQ was like walking through unknown territory equipped with blinkers right and left, thus staring forward to one target: how to uninstall the corrupted KWallet. So I stumbled anywhere upon an article containing the solution of my actuel problem: folders -> /usr /share -> delete /kdewallet. Newly to install it (with the possibility to edit a new password) was recommended to use aptitude.
You see, I am not the right adress to inform and instruct the world - for not a short time further on!

this is not a clean way of uninstalling anything.
in fact you haven't uninstalled anything, you just deleted a few files that kdewallet needs.
i wonder if you could locate kdewallet in your softwaremanager and uninstall it from there?

no doubt it will raise some flags because
- you already destroyed the installation.
- kdewallet likely belongs to the KDE desktop metapackage
- there might be other applications depending on kdewallet.

it would be better to fix this, or at least to not see it as a succesful model of fixing things on gnu/linux.