Trouble installing .air app on mac

For the sake of people searching, or if the image gets removed on day, here is the error message as text:

"Sorry, an error has occured.  The application cannot be installed due to a certificate problem.  The certificate does not match the installed application certificate, does not support application upgrades, or is invalid.  Please contact the application author."

I keep getting the above error when trying to install a new .air desktop file on a third-party Mac over which I have limited control.  The .air app does work on Windows 8.1.

-Do you think it could be the AIR runtime (currently version 14, and am getting admin to update it to version 16)?  I built the app in AIR 16.

-There is a previous version of the app, with a different certificate that is already installed.  Would this possibly cause the error?

-Finally, I signed the app with a self-created certificate for development reasons.  Is that likely to be a problem, it didn't seem to be an issue last time I did this?

Thank you.