Sims Medieval cannot take Pirates and Nobles, error says base game is not updateable

Hello. I am hoping you can help me, since I found here the only working help for the Launcher issue, after many fruitless exchanges with EA unspeakably abominable customer support.

Now I wanted the Pirates and Nobles expansion and I bought it. Made careful by previous problems, I decided to buy the PACK from Origin that contains both the base game and the Pirates and Nobles expansion, thinking that so I would be guaranteed that it all worked. After all the game is sold as being specific to MacOSX Leopard and higher, and I have Lion.

So, I uninstalled the old game (made a backup of my world data) and reinstalled the base game that I downloaded from Origin in the pack. The installation went well (aside from reviving the Launcher issue, for which yet I have a fix, so NP).
But when I try to install the Pirates and Nobles expansion (which came IN THE PACK with this same base game) it gives me this message:
The Sims Medieval™ Pirates and Nobles Compatibility error
The version of The Sims Medieval™ installed is not updatable and is not compatible with The Sims Medieval™ Pirates and Nobles.

This is driving me crazy. Is there anybody who can help?