Sims 3 Dreams Island freeze

Hello everyone.

Yesterday I bought the Sims 3: Island Paradise expansion pack, I already had Pets and Seasons.
I installed it via Origin, so without the CD and using the serial code.
This morning I started playing, I created a new family with just one Sim.
At first the game runs well, but a little later there are kind of "freezes" where the game locks up for about 10 seconds. It's mostly my Sim that freezes, there is still sound, and the landscape moves around. The freezes happen very often and it spoils my enjoyment of playing..
My graphics settings are not too high.
I also tried resetSim and nothing happened..
I didn't have this problem before, it's only since Island Paradise.
My graphics card is up to date.
I also tried playing with a save I had for a few weeks in Appaloosa Plains, and the game doesn't seem to freeze at the moment..

I really need your help.
Thank you very much :)