How do I get the Hogwarts History book on Harry Potter and the Chamber of Secrets ps2 game?

I'm on the very last stage, and have called hedwig. She has let down a ladder, but either I can't find it or the one i have found, by a door covered in green slime, does not complete the puzzle. After goin up this one ladder, and around the tops of the cases, i find myself a jump away from an overhanging, that is blocked by a piece of rope. Am I missing something in this stage? I tried jumping onto it, but I'd only land it once out of maybe 12 times, and when I DID land it, it wouldn't let me pass. Help please!!!