Lately I haven't been able to select my pre-made Sims in CAS. After doing some research, I've learned other Simmers have been having the same problem. After re-installing my game(s) and still having the same problem... I realized it must have something to do with the latest patch (1.55) update and/or a mod in my game and luckily, I've finally found the solution...
As with any core mods, controller mods, or hacks (mastercontroller, slider hacks, etc.), be sure to UPDATE any mods after receiving an EA patch update through the Sims 3 Installer.
If you have Twallan mods or NRAAS mods in your Mods>Packages folder, be sure to download the latest version from their site.
Once you've done that, you should be able to play your Sims 3 game(s) with no problem!