I finally had to look it up myself. In the ADT 3.3 FAQ, it is in section
8, and the answer is:
AECFILEOPENMESSAGE
Now I can set it up right.
In hindsight, I realize that this was not the right group post this in.
I thought it was general AutoCAD, but it really is an Architectural Desktop
issue. Objects in R2 drawings are different from objects in R3.3 drawings
and it has nothing to do with vanilla AutoCAD. My mistake.
If a moderator runs across this posting, feel free to relocate it the
aec.arch-desktop3 where it would more appropriately belong.
Thanks,
~SirCasey