Hey q,
What page are you downloading from? Also, what's the 5 digit # in the file name just before .dmg?
I just tried downloading from the 10.3 page and 10.3.1 page and they work fine.
http://avid.force.com/pkb/articles/e...10-3-Downloads
http://avid.force.com/pkb/articles/e...-3-1-Downloads