A friend I have downloaded it for Mac and it worked for her, but the same thing happened for her sister. After parental controls had been turned off it worked, so you may want to make sure there are no parental controls on and possibly check your firewall (If you have one) Is all working right.
I don't know a lot about Mac's but you may want to try running as Administrator if that exists for Mac...
(I don't know if Mac's have that)
Hope you get it fixed.
