Owncloud Windows: lost a whole album sync and can't re-add it

Hello
Let me help you since there is so many helper here and no one cares about why suddenly a program removed an important part of its own config file:

Check The folder ..... is used in a folder sync connection! Please pick another one - #2 by michaelstingl
I have renamed all owncloud technical files in the local folder and re added that folder for sync