when you are in studio 8 take down the front wall all the way down to the door there in the hall serve food and throw party worked for me.
I did that and after everyone left it showed that I had a succesful party but when I checked the goal, the goal still had not been complete and then the next (in the game) day, charity ask me AGAIN "don't you think it's time to re-arrange things to host the art show?" ARGH!!! What am I doing wrong. It's about to drive me crazy...enough to want to quit playing game!