Re: Cant run game after installing EP Seasons...

This is not an error.  This is how the game works.  

After you install the base game and expansion packs, the launcher will always ask for the most recently released game; not the last one you downloaded, but the last one to be released.  In your case that's Seasons.  To play the game, you need to insert the disc it's asking for.  When you get to the main menu all your worlds will be available for you to play.  That means the worlds from the base game, Late Night,  Ambitions, and Pets will be there to choose from.  World Adventures and Seasons do not come with worlds but their features will be in the game as long as you installed.  You will always have all the EPs available this way.  Does this make sense?  I hope this clears things up.  

edit: grammar :D