We just released the beta of version 7 of our VB6 based app. We have
documented how to write a VB.Net addin to extend our functionality and
it works just fine using the version 6 release.

One of our beta sites who has written and is selling a .Net addin for
the v6 tried to make his very same dll work with our beta 7, but it
failed with a "QueryInterface for interface xxx._yyy failed" error. I
can recreate the error here in the plant.

To complicate things, the beta site was sent a copy of the upgraded app
compiled without binary compatibility being set, and we thought that
might be the problem since the .Net DLL has a reference the original app
(for access to data class definitions used in the DLL). However,
recompiling the DLL with a reference to the correct executable (with
comptability set to the v6 app) and the problem still appears.

Any clues?

TIA!

    Bo