I can have my own proposals accepted just fine, but whenever I attempt to accept an invitation to dance from the link on my sidebar, I receive this error:

... regardless of who actually invited me to dance. ( sent me an invite to help test this, and they haven't blocked me, but I got the same error when I tried to accept their dance proposal.)

Heeelp? ;w;

Dances get accepted in the order they've been sent to you, so if you have leftover dances from previous years, those would get accepted first and that's probably the one (or ones) that are giving you a problem. I'd try filing a ticket and see if they can clear the ones from users who have blocked you

Ah, that makes perfect sense, then! Thanks so much. :)