Hello Sabeshan,
Thank you for your answer. Right when I was about to contact Esri Support, I realized I probably did not use ArcGIS Editor, but ArcView. Switching to ArcEditor did the trick. This is rather embarrassing. However, the strange thing is, I was able to create a BIS, change metadata settings, create data collections and all in ArcView. Only when I tried to add bathymetric data I received the message posted in the title of this thread, which did not give any hint where to look for the problem. Because everything seemed to work at first, it took a while to realize I was using the wrong ArcGIS Version.
Sorry for any inconvenience I might have caused.
Cornelia