Earlier today I updated wow and the adibags addon. Now, when I try to open my bags, I get these error messages:

There are separate versions of AdiBags for each game client (Classic and Retail). You appear to be using the wrong version for your game client.

What the heck....that's exactly what the problem was. I don't know how it happened -- updated a bunch of addons via Twitch today, and they all updated with the Classic versions...

Thanks for the help!