I get this error when I'm trying to do the signup for the "Stealthy Sionnach" on the bulletin board. Not sure what it means, but the last time it happened I didn't end up getting a Stealthy Sionnach gift from anyone.
I also got this error! I do not know what causes it either.
EDIT: It stopped me from completing the best friend favor scene (when you get to the point of selecting between how you feel about sleeping in the same bed) and brought up this error. I'm playing via Windows 11 on the itch.io app. I could not select "You feel some things about this" after this pop-up, but I could click on other things.