Application xxx could not be launched successfully

For the first time in about 6 months, we're updating our AWS application (with no environmental type changes at all). But in the 'configure' phase of running the Appstream 2.0 Image Assistant, when we try to start the app, we immediately get a dialog box that says "Application xxx could not be launched successfully. Check that the application was installed properly , does not require elevated privileges to launch, or is not part of a user folder hierarchy."

We can execute the app successfully out of its 'C:' drive home just fine, up to the point where it needs the environment as set up by Appstream, so we don't think it's anything to do with the application itself.

And in any case, we haven't changed anything outside the standard functionality of our application. We haven't been able to find any useful references to the message via a web search. We're wondering if there's been an Appstream change in the last 6 months or so (and what to do about it if so), or if anyone has any ideas about what might now be wrong.

Thanks!