How to Create a Datum Definition in Map 3D

[Pointdump]

I can create Projected Coordinate Systems, as long as it's based on an existing Datum in MAPCSLIBRARY, but all my attempts to create a new Datum have failed. I always get the "Cannot Save Projection Code to Drawing" Error. I've tried both "Create A New Datum" and "Create A New Datum From An Existing Datum" using instructions in >>>Map 3D Help<<<.
I'm trying to create Slovenia 1996 / Slovene National Grid, >>>EPSG:3794<<<, which is based on Slovenia Geodetic Datum 1996, >>>EPSG:6765<<<. So how would I create that new Datum Definition?
Dave