Hi there, and welcome to NRaas. Sorry to hear that MC is crashing the game on you, this is not typical behavior of that mod (or any from here) at all. Let's see if we can sort this out.

-- What patch level is your game on and which exact version (e.g., v133) of the MC base mod have you attempted to install?
-- Whenever the contents of Mods\Packages changes in any way, the five cache files in your TS3 game folder should be deleted. The most important one here though is the scriptCache.package file. Have you deleted that one before attempting startup with MC in place?
-- There is actually a common cause for the crash on startup, and that is when players include the MC Progression add-on module but don't realize that one requires both the MC Base mod and the StoryProgression base mod. Sounds like not the case here since you said base only, but just confirming that MC Progression is not part of the problem.

...and possibly some follow-up questions pending the answers to the above.

I take it you meant both base mods (core mods are something different).

Okay let's just confirm this, your game itself is on Patch 1.69, which means it is Origin-controlled. And you are using version 133 of MasterController base mod, not one of the older ones, correct? I would suggest discarding the MC mod, download it again just to make sure you didn't get a "bad" or corrupt download the first time, clear the scriptCache file, and try to startup again from scratch with no other package files in place at all. But try to startup a new game in Riverview, not your ongoing saved one.

Couple of follow up questions, though.
-- What was the original source of your game and it's EP/SPs, were they all Origin digital downloads, retail discs, a mixture, from someplace else (where)?
-- Any third party game "helpers" or hacks in play, not from here?

Direct link to MC base mod, ver 133: <a href="http://nraas.wikispaces.com/MasterContr ... +Twelve</a>

No, I meant other things that are not so removable but if you don't know what these are then I doubt you have them.

I take it that you are selecting the EP/SPs required to play on the 1.69 Launcher's Packs and Stuff chooser tab, so as not to be starting up a game that has seen, let's say Pets, without the Pets EP in play.

So try the run on a freshly downloaded MC base mod only, starting up a new world.

If that still crashes (hope it doesn't), the next thing to try is to pull your entire TS3 game folder out of Documents to your Desktop for safekeeping, start up the game to allow the generation of a fresh game folder, back out, redo the Framework on it (Packages, Mods, Resource.cfg file), and start up a new game on the fresh folder. If it works, add MC base mod only to that, clear caches, and see if that one works. You won't have any downloaded content at all, no other mods, store or custom worlds, saved sims, lots, or saved games, etc. but those will all be safe back in the pulled out game folder and can be put back later.