Did you buy your Sims 3 for mac game from Bigpond games Australia? Do you know anyone else who has?
The game comes with the mac and windows versions on the same disc, so saying "for mac" is slightly pointless. I could see a one in a bazillion chance that you got the one disc with a corrupted version of cider on it, but that is unlikely and I mostly don't buy it. Stranger things have happened, but I honestly wouldn't blame the store you got it from in the event you did get a bad copy. I am curious if it works fine on a windows box though.