no binary compatibility file set?

I have 2 project in a project group
can i make them into a single .EXE??

when i try to make exe, an error pop up and tell me:
"the project "Project" can not be built because its references project
"path\...path\ABC.vbp" which does not have a binary compatibility file set."

what is the problem ?
I cannot make 2 project into one .EXE ?

another problem are about the OS(?)
my program run well in Windows 2000,
but when changed to windows XP,
there is an error "Active X cannot create object"

sorry if the question is too "open-ended"..

I always apply 'KISS' so I never create project groups.
And I always have all the constituent modules and forms, in the very same folder as the vbp file ('KISS" again).
But every so often I download an example where the author has designed his as a VBG
So I am curious as to the answer as well.