Bean122 Try deleting the folder for one of your packs and reinstalling it. Wherever you installed the game, you'll see a Sims 3.app and a "The Sims 3 Packs" folder, which contains one folder per pack you've installed. These are numbered by type and release order, for example Seasons is EP08 because it was the eighth expansion released.
Point is, delete one of these folders, run the EA App recovery tool (under Help in the menu bar along the top of the screen), restart your computer, and download the pack again.
If this doesn't help, please let me know what exact drive you're using, and whether you've connected it directly to your Mac or have plugged it into an adaptor or hub of some kind.