There are two possible reasons this is happening.
The download could be corrupted or incomplete. Redownloading the file isn't a bad idea to get a good copy. However, if you don't clear the cache and cookies, your browser will probably just give you the same file again.
This article gives tips for redownloading: Answer Title: What are some general tips that I should follow when downloading a product?
Answer Link: https://helpdaz.zendesk.com/entries/123812-download-tips
The other possibility is that another software on your system is conflicting with the Bitrock Installer. This one is a bit more involved to deal with. You should make sure that your antivirus and firewall are disabled for this part. If that doesn't work, then you should boot the PC into SAFE MODE (not safe mode with networking, just safe mode). Often, even when an antivirus or firewall has been "disabled," software modules for it are still running and can still interfere with other software.
To put your PC into Safe Mode, restart your PC and tap on the F8 button until you see the option for SAFE MODE. Choose 'SAFE MODE' and press enter. When given the choice to log into an account, choose an account with admin rights.
In safe mode, try to run the installer. If it runs in SAFE MODE, that is fairly strong evidence that an application or software in normal mode is conflicting with the Bitrock installer.