Lego Harry Potter (Years 1-4) Wii Help...?

I have 199/200 Gold Bricks. It appears that the last one is in the Restricted Section of the Library. The bit where you need an ageing potion to get in. However, the Gold Brick Finder shows me no extra bricks, whilst the Hogwarts Crest Detector says there is something by the bookcase to the left of the large door. (The indicator is yellow, so I ume this must be the last brick, or whatever) I have found all the crests in Story Mode, and I was wondering if anyone else has had this problem, and if there is any way to fix it. I thank you in advance for any information you can give me...