Lately Ive noticed that, no matter what I do and how careful I am, after some time playing a save the game keeps crashing or lagging, or I often cant save and error 12 comes up. At this point Ive just started trying to save more frequently, but I wonder whats the cause of all this? Since I had to reinstall the game several times to get it working on this computer, the files were turned back to default many times. I wonder, is bad cc still a thing? I know its been a long time since they were a very big problem but I did find that cursed doll but with a weird realistic face in my game many reinstalls ago even though I never installed any nursery set or whatever. But I no longer have that doll in my game, and I have no idea what causes all these errors to be honest

Error 12 often means the game has gone over 3.7GB of RAM usage and will no longer save. The game with all its assets is of course much larger than that, especially with store content and mods, and is constantly loading and replacing information from storage, as you're playing the game and moving around in the world.

The game isn't perfect to put it lightly however, and will slowly creep up to that 3.7GB and basically crash at that point. Actually it will just refuse to save, but that's worse than crashing.

There's a bunch of things you can do to alleviate and postpone the error though. With these precautions I basically never get them anymore.

Never leave the house without NRaas Saver. I have severe trust issues with TS3, so I set my autosaves to 15 minutes. No matter if the game crashes or error 12s out, you only lose 15 minutes progress at worst. It also has a feature to automatically switch to map view during saving, which can bring RAM usage down by about 100MB and potentially salvage an otherwise hosed game. It also also nearly automates the process of never overwriting an existing save, and always doing a save as.

Lower the graphics settings a bit. This may be the biggest one. I don't want to live without very high Sim Details and Visual Effects, but everything else is set to low-mid for me. 2 High Details Lots.

Immediately save, exit, reload after traveling.

Prefer smaller, less stuffed lots to play on.

Cleanse all the useless thumbnails taking up space in your save file with the first two options in Regul Save Cleaner.

When quickly switching between households with NRaas mods, regularly check if no inactive households are accidentally left "open", and use City Hall->NRaas->Master Controller->Town->Drop All Dreams And Opportunities.

Lastly, just don't play enormously long sessions if the errors persist. Save, exit, load back in every 2,3, whatever works for you hours. Keep an eye on the Commit (KB) value for TS3W.exe in Resource Monitor.