Sorry I didn't reply sooner, I had a few very busy weeks.
The total project incl. assets was about 1Gb in size, so I couldn't just upload it.
I've tried to isolate the problem, I did not succeed, as soon as I reduced the project there was no problem rendering, it didn't matter what parts of the project I deleted.
I guess it was a weird coincidence, it just happened at the wrong time for me. I managed to render all scenes by deleting all inactive objects for the specific scene, which is strange, I never had to do such a thing.
It was a 90 sec animation, after rendering I had about 2 hours for the compositing, including render and compression, to get the animation on time at a presentation........
Cheers
Hans