I am stuck on the Just Desserts portion of Lego Harry Potter Years 5-7. I have gotten all the way to the Christmas Ball, and have gotten the lamp off Hermione, gotten her out of the pumpkin tree, taken the platter off her head, and now I am to the part where I put the green knobs onto the back curtain. Using Winguardium Leviosa and both Harry and Luna, I still cannot get the curtain to open. I have gone back and redone this level from the beginning four times, and still cannot get the curtain to open. Does anyone have any ideas on what I can do to get it open? Thanks.