Purchased Base Game - Can not install any expansions. [SOLVED]

I have a purchased copy of the Sims 3 base game. I have only games4theworld downloads of the expansions. I have mounted all of the images and installed the base game correctly and can launch it. No matter which expansion I attempt to install I receive an error that says I need to install the Sims 3 first. I have the most up to date patch and have searched the forums for hours trying not to have to start a thread as I usually can figure these things out. Please help! It is a rip off to spend 400 bucks on the expansions.

Well, first off, what images are you mounting? There's no disk images to mount in ANY of the g4tw expansions, only the base game.

Secondly, where did you buy the base game from?

Base game is from Steam. I can't get past step 1 in the instructions guide.

//EDIT

I have unmounted the files I mistook for needing it. Sorry about that. I
am still running into the same error that I need to install the Sims 3
before I can add expansions. I have uninstalled and reinstalled twice
today.

It's because the base game is through Steam. There's no way to add on other expansions with a Steam game, even if you owned the disks. All expansions need to be installed through Steam.

I uninstalled the base game that was installed through Steam and reinstalled it after downloading Origins. Found the game in Origins and installed it there, didn't need anything to do it except being registered. This allowed me to install all of the expansions and it is working great as far as I can tell.

Good. Glad you found a work-around, and I'll have to remember to suggest going through origin for other Steam users.

Glad that I figured it out! I hate Steam... Hope many people get resolution from this result.

Steam is awesome for multiplayer games/games with no expansions. And for sharing games with friends ;D