O.K.
I did some research and i found out that my previously created „streams“
subfolders with numbers from 1 to 14 were gone?
sudo mkdir -p
/opt/open503/webapps/openmeetings/data/streams/{1,2,3,4,5,6,7,8,9,10,11,12,13,14}
Also the owner of some other „number Folders“ were wrong root:root.
I recreated the Folders, changed owner to kurento:root and now i can record.
Can it be, that those Folders were deleted using the „cleanup“ function?
But there’s an other Question coming up:
Is it possible to only record the Whiteboard but not the rest of the window?
POW