I am having trouble getting Seasons to install.

The Disk loads fine.
The installer seems to work fine going through all the steps etc. (including installing into the correct folder)
I do however get a warning saying that this the game is more up-to-date than expected and this can cause Seasons to be incompatible. (I am assuming this is where the problem lies but have had no problems up until now installing expansions after patch 1.67)
The installer will run very quickly through the 91 files (in under 2 min. which in my experience is way too fast)
The game will load fine. It will not load from Seasons disk but from Generations which up until now is the most recent EP that I have installed.
None of the seasons content shows up in the game. Not even in hints which means the game just doesn't think it exists.
It does not even show up in the uninstaller menu.
I originally installed the 1.67 patch onto the base game and since then have installed 3 other EPs afterwards all of them much older than Seasons (in the order they were installed: Generations, Late Night and then Ambitions)
I saw some allusion on other forums that the order of the installation matters but so far this hasn't been a problem.
I am also using a Mac (bought within the last year)
I have tried reinstalling Seasons now 3 times each with the exact same problems to no avail.

any ideas?
and also if this is just the patch version any ideas how to get around this without having to uninstall everything and redownloading all patches individually?