Make sure the download isn't corrupted and that you download from
the official site only.
To check if your download is legimate and not corrupted:
1)
Right click the setup file in Windows Explorer and choose "
properties"
2) Go then click on the "
Digital Signature" tab
3)
Select the signature in the list.
4) Double click the selected signature or click on the "
Details" button you'll see under the list.
5) The signature is being validated now, and a next screen is shown. On top of it you'll see if the signature is ok or not. If it is not, you have a corrupted and/or infected setupfile...
note: firewalls don't cause these kind of problems. Faulty downloads with download managers, tools to "speed up" downloads and virusses are the ones to blame...
/ 
