I made a copy of the table for the subsite and everything appears to work. The summary widget on the admin dashboard shows the collected data. As far as I’m concerned this is fixed.
Thanks for your time.
Thanks for getting back to me. I think I know what happened. The website in question is a subsite on a WordPress multisite install. When I installed the plugin it created the subscribers table for all of the subsites, but only created the activity table for the root. I didn’t see the table until a couple days ago when I was doing some cleanup. My guess is that you don’t officially support multisite, at least not on the free version, which I completely understand. It looks like I can probably just move or copy the activity table to the subsite and the error will go away, or uncover a new one.
Again, thanks for getting back to me.