Ok awesome, thanks guys! I think we’re getting somewhere….
To answer your first question Wayne, yes it does the same thing with a fresh file, on the default cube. I reset back to factory settings and that actually seemed to resolve the issue. I was able to insert keyframes as expected.
I downloaded 4.1.1 after that, and kept my old user preferences, and I was getting the error messages again. So I then reset back to factory settings again in 4.1.1, and keyframe insertion works again.
So I think we’ve narrowed it down to something in my setup. Now I can at least work from zero and re-enable my add-ons one by one to see if any of them are the issue. I’ll be sure to use this troubleshooting method in the future =)
I could still post the Blend file if that would be helpful for any reason.
Thanks a ton for your patience and assistance!