This message means that some datasets with the same prefix but different views (such as fred+orig and fred+tlrc) are marked as having different "types" of data -- one is marked as an anatomical dataset and the other as functional. How that happened, I could only guess.
It used to be that AFNI strictly segregated functional (overlay) and anatomical (underlay) datasets. This is no longer true, and the code piece that you've triggered is something leftover from those days. I can remove this hiccup/error when I return (I'm in Taiwan right now), but as far as I know you are the first person in 15+ years to report this message. Clearly something happened to one of your datasets, but it's hard to say what.