Try to resave/download the file (I know it's a bit big) and only leave it on your desktop. You may want to use WinRAR as I know that WinZIP has had compatibility issues with .rar files in the past~
I've heard a lot of bad things about WinZip and wasn't planning on downloading it, but I always mistake WinRar for WinZip and vice versa so I kinda stumbled onto the one I didn't want to download. XD Thanks~
EDIT: Oh, looks like re-downloading the OST did the trick. o_O Yays!