I have this Output.
Cannot write to file /home/sven/.kde/data/stalefiles/kdenlive/Von%20ersten%20Versuchen%20bis%20Heute.kdenlivexBMfile_%2Fmedia%2Fhome%2Fkdenlive%2FMeine%20Gleitschirmfliegerei%2FVon%20ersten%20Versuchen%20bis%20Heute8AlJyxBM
What does it mean?
What must I do with that?

Greetings Sven

It is a message of the "Crash recovery" feature of Kdenlive. There is a bug on some systems that triggers this, see our bugtracker:
http://kdenlive.org/mantis/view.php?id=2441 and http://kdenlive.org/mantis/view.php?id=2450

This should now be fixed in latest git, I am waiting for feedback. As a workaround, you can disable the "Crash recovery" feature from Kdenlive's settings dialog.

regards

It is one of the latest Versions..
But it is an old Projekt..

Greetings

If you are using the sunab expertimental repository, it usually compiles daily, but depending on when the change is made, it can take 1-3 days before that change reaches the sunab package.

regards