Did you download the whole file which is about 1GB ? And is your extractor up to date ? I won’t be downloading it again to test it.
If you have downloaded the whole file and you are using up to date extraction, and it still won’t open, try repairing the zip file, most extractors have a repair tool.
If that doesn’t work, the quickest way to get help would be to go and find Christian anywhere on the net except for Pianobook and contact him that way.