It is easy to miss a bad file size. In Windows Explorer, right click on the pane, and selected View > Details in the dir you downloaded to.
Slowly scroll down the list until you notice a little something different go by in the listing. If so, take a closer look.
Only part 406 is less than 1 megabyte, and should be 589kb. All the rest should be 1,024kb in the list.
Move all the parts higher than the bad part to another dir, and delete just the bad part. Now start the Downloader and let it get the one that you deleted.
Now, go the the dir where you saved the good parts, and copy them back to your download dir. If you have more than one bad part, do
this until they are all good.
You will need to delete the corrupt zip file that was made before
you got the new parts, as well, I think.
This worked for me, and I replaced two bad parts and installed FPSC without trouble.
-JerBil
Ad Astra Per Asper