Gnat's "Missing Subunits"

[prichtmyer@yahoo.com (Peter Richtmyer)]

I am trying to compile a very old, large VAX Ada system using Gnat
3.15p
(Win2000) on a PC, hoping to modify the old system enough to do a
little debugging on the PC.

Sometimes when compiling a large Generic Package body, I get no errors
except "missing subunits". I have found no easy way to identify 
the problem(s). It seems like the problem is sometimes actually in
a "with'd" package a couple levels deeper.  

Is anybody familiar with this, and have a way to find the problem(s)
quickly? 

I wish it could tell me what "subunits" are missing. I have looked 
through the docs but found nothing on this subject.

Thanks,
Peter