There have been reports of Windows users having issues with the purchased download but I haven't seen the exact problem you've described. Submit a request to let support know.
In the mean time, there were old issues of corrupted downloads caused by firewalls. Though we've not seen complaints about that in a long time, I would disable any or use a different browser to download again.
This is a Users board. MakeMusic Support almost never responds to posts here. That's what the Submit a request at the top of the page is for.
When you do get a solution, please post it here. That will help others as this thread will show up in a search engine if someone else has the same problem.