Are you attempting to run directly from the download?
I've definitely seen instances of antivirus, including the version you
mention (at least via these groups)--apparently interfere with
installation--i.e. running the downloaded file, once the download completes.
I don't believe it should interfere with the download--but there have been a
number of reports that seem to reflect incomplete downloads--and I don't
have any feel for common factors among them.
So--I'd recommend downloading again, and saving to a known location. You
might even download twice, if your connection is fast, and comparing the two
files.
Then disable the real-time protection from the antivirus for long enough to
complete the installation.
