Firstly, thanks for all of those who suggested various causes and fixes.
The issue was finally resolved and it was one of those very annoying ones where the only symptom I was seeing that Nz stopped working but the cause was larger.
It seems that something happened during the latest software upgrade that screwed up Access itself. I removed it from the PC completely, rebooted, then reinstalled it. The problem is now gone.
I apologize if anyone spent too long trying to puzzle this out. Since the rest of the features seemed to be trouble-free, it never occurred to me that Access itself needed reinstaling.
The issue was finally resolved and it was one of those very annoying ones where the only symptom I was seeing that Nz stopped working but the cause was larger.
It seems that something happened during the latest software upgrade that screwed up Access itself. I removed it from the PC completely, rebooted, then reinstalled it. The problem is now gone.
I apologize if anyone spent too long trying to puzzle this out. Since the rest of the features seemed to be trouble-free, it never occurred to me that Access itself needed reinstaling.