Ok,So I have the Sims 3,plus all expansions, and i successfully installed the base game, world adventures and high end loft stuff (all updated to the latest version)!!!!!

Now when, i try to install ambitions and the remaining expansions,it says THIS PRODUCT REQUIRES AN INSTALLED COPY OF THE SIMS 3.

Thats the problem i have already installed Sims 3, So why cant I install Ambitions and the remaining expansions?

You have to update it to the latest version(open launcher and wait for a question to install a new update).If you did that and it still doesent want to install the try uninstalling the entire game and then install ambitions then hi-end loft stuff then world adventures.It has something because ambitions was the first sims3 expansion so there may be problems with that.I installed that way and it works for me.Hope it helps