Hi Ralf,
I have found the error myself.
My license includes 10 users. In the DE instance I had already created 18 users. The trick was: deactivate 8 users, do the migration again and voila: It works!
Btw: the update from 2.4.x to 2.5.5 also worked seamlessly.
Thanks for the quick responses. Your product and team is great!!!
KR Daniel
