Seasons Install "compatibility error"

Hello ! I just found this wonderful site and the first thing I did was to download the new Seasons add-on, the manual update patch and the Fix.
I installed it on a buggy game, so without surprise it didn't solve anything and it kept on crashing (the nasty "exception raised"). I had LOTS of pb with my game, even though all of the disks are legit. The only one I downloaded is Seasons.

So, I made a clean uninstall of all the Sims 3: I deleted preferences etc. Then I re-installed all of my base/add-ons (I have all add-ons except Ambitions and Seasons, and none of the stuff packs).
Then I wanted to install the Seasons add-on I downloaded. I extracted it with Stuffit and put it on a new image disk as recommended.
When I launch the install, I can enter the serial but then I have a message error telling me that there is a "compatibility error" with the game, and that The Sims 3 isn't compatible with it. Then I can't continue with the install.
Why does it happen?

Did you apply the manual patch before trying to install Seasons?