Dear Werner:
I would need to see your model to determine what is wrong with it. However, note that you need to have a completed HEC-RAS model for the HEC-RAS floodplain mapping to work.
You can email me your model if you want, and I will check it out.
Also, inserting a "part" is the same as inserting a "block", as it is in AutoCAD. The RiverCAD CAD engine refers to "blocks" as "parts".
Sincerely,
Chris E. Maeder, M.S.
Senior Technical Engineer
chris.maeder@bossintl.com