Yep, I've had similar problems, especially the freezing for a minute or two.
The error message for Error Code 12 is misleading, and what usually produces it is running out of memory. So, save your game often and make sure you turn off all non-essential background tasks before playing TS3. I got Error Code 12 all the time when I tried to play a Stylist, because the game kept track of all those new outfits for all the NPC's, which was a big strain on the memory. Adding more memory to your computer is also an option, unless your computer is already maxed on memory.
For me at least, Showtime is glitchier than previous EP's have been, but it's a fun EP, so I put up with it.
You could try installing Twallan's Overwatch mod, which is supposed to catch errors before they break your game, and see if that helps.