I managed to find the source of the Problem. During the last upgrade the Java stack itself had been upgraded but it seems as if the Adobe Document Service had been forgotten. So we currently use a Netweaver 7.3 SP1 together with an ADS 802.*
There is a workaround which ssems to work until we can do another upgrade:
Change the target Version of the form back to version 8, save, and Change it back to where it was before. After that the form get printed correctly.
Best regards
Michael Biber