Solved by workaround.
I had a reference system where bp is working with release 7.31 whereby I configured the other system.
In xo80 you have to switch to SAP mode to be able to add a new business_partner otherwise it won't allow because of naming conventions.
Furthermore I exported a xml-file from that bo-object within the xo_cockpit and was able to compare it to the system where bp is working. There I could get hold of all the tables involved which I synchronized by "brute-force" by se16n table by table.
At the end I had an working bp at last.
Kind regards