Thanks for the answer.
You are right, I forgot that there is a tool for it.
I tried it, but it doesn't work either. But the error message is different and it seems a version issue at the moment.
The Engine to be converted is a VM version 5 and the first engine was at version level 6.
Converter 5.5. needs a version equal or higher to version 7. Why the VM on version 6 was converted successful was a lucky chance.
Now I will first upgrade the VM Version to version 7 and start it again. I will come back with the results.