Actionscript 1.0 is no longer supported dialog...

This dialog started showing up today. Never seen it before.
I've been working with Animate for 20 years. I have no Actionscript 1.0 code in my docs, and even if I create a brand new doc, create only one Symbol in that doc, close and reopen, I still get this.
This is driving me nuts, as it presents four times every time I go to debug. And it is very slow to respond.
Please tell me how to get rid of this!
