I have isolate the problem. The error appears only if by the last run of ImgBurn the Checkbox 'Close Program' was checked respectively the cli argument /CLOSESUCCESS was used. So if ImgBurn is closed manual, the next time i can burn without getting the error.
What's the meaning of 'Device Not Ready (Logical Unit not ready, Long Write in progress)' thats shown in the video and are the dvd's nonetheless burn accurate?