Does the download actually complete (i.e. you get a 100% reading) or does it stop somewhere in the middle?
If it stops somewhere in the middle and doesn't download completely, that is why it's corrupt.
Not sure which browser you're using (I'm assuming IE from the sound of it), but you may also want to try using a different browser too. If you're using IE, try downloading using Firefox instead.
Hope this helps
Pat (ala Jeeper One)