@rellietay What you've described is a bit more work than is necessary. The idea here is that your newest pack (by the date EA released it) runs the game to some extent, so it needs to have access to files from other packs in its own folder. Most of the packs install correctly, and the proper files are moved, or rather, aliases are created that point to the proper files. So, for example, right now you only have WA and Ambitions installed. If you open TS3's package contents and go to Contents\Resources\AddOns\Ambitions\Contents\Resources\transgaming\c_drive\Program Files\Electronic Arts, you'll see a folder for Ambitions's data and an alias that points to a folder for WA's data. So Ambitions can access WA's content while the game is running.
If you were to add HELS, a pack that installs correctly, an alias for a folder containing HELS's data would land in the same place as above. HELS is older than Ambitions, so Ambitions would still be running the game. If you installed Late Night, the proper aliases for WA and HELS would land in LN's version of the program files in the path I described above. But there would not be an alias for Ambitions, so you'd need to create it yourself. The instructions say to paste the entire folder; I've never tried making an alias instead (maybe I'll do that the next time I'm testing something). Regardless, the point is that inside LN's package contents, there need to be references to the data for all the other packs.
If you install a later pack than LN, that pack will run the game, and you'll need to transfer over the files from BOTH Ambitions and LN. If you install IP, that's where the folders go, if you have Generations but not IP, Generations needs to contain those folders. Again, you don't need to do anything for the other packs besides Ambitions and LN; the install process takes care of that. And there's no need to copy the folders onto your desktop, or anywhere else, before you install more packs. You also don't need to make a copy of the folder for your newest installed pack, whatever it happens to be. So if that's LN, you need to copy over the files from Ambitions into LN but don't need to mess with LN itself.
If you're still having trouble, just remember that whichever your newest pack is, it needs to contain references for every other pack you have installed. If something is missing, follow corey's instructions to go find it and copy it over.
