What exactly happened when I tried to download this? I got prompted by my anti-virus that this game was trying to put a Trojan virus onto my PC and the download did not continue. Is there going to be a fix for this, and better yet, what is the cause???

It is a false positive I refer you to GoG's support page about it.

http://www.gog.com/en/support/the_chronicles_of_riddick_assault_on_dark_athena/virus_warning