Error Code 12 in "The Sims 3" is described in the game's documentation as a "world save failure." What this means is that your computer had insufficient memory to save the game's world file, causing a save failure. Freeing up resources during a "Sims 3" session is usually the best way to treat the problem, but you can generally also prevent the error and even correct it by changing your saving habits.
Close Resource-Draining Apps
When you strain your computer with too many simultaneous tasks or processes, its performance suffers. Games like "The Sims 3" are resource-intensive, especially on higher graphic settings. When you run a lot of other tasks in the background, like media players and Web browsers, it can bog down your computer. Closing out any programs you don't need can reduce this strain. You should also avoid playing "The Sims 3" during resource-intensive tasks like anti-virus scanning or while running other resource-hungry programs like Adobe Photoshop.
Try to save during periods of low activity in your city, ideally at night while your Sims are asleep. Putting the city into edit or pause mode can also help ensure a successful save. You should also never use save and quit; instead, save the game normally and then quit without saving -- this process is less intensive and less likely to result in a corrupted save. You should also avoid using spaces or special characters in the save's file name.
Other Useful Habits
Avoid long, continuous gameplay sessions, and instead save, quit and restart the game at regular intervals. If you've designed any Sims that you no longer play with or have any use for, delete them to reduce the amount of data needed for the save. If you have a lot of excess items in your inventory, remove them to reduce the number of things that have to be loaded.
Correct Save Failures
When Error 12 occurs, the save file will be relocated to a new folder and given a new extension: ".BAD." These files will never work properly again and should be deleted. Once this happens, use "Save as" instead of "Save" and create a new save file with a different name. Used in conjunction with smart save habits, you should be able to recover your city and Sims. You can also move your saves folder to another location, like the desktop, and try creating a new save. If nothing else will work, you may need to quit the game without saving and restore your saves from a backup.
Updates, Reboots and Defrags
A regular reboot schedule is a good idea, especially if you are in the habit of leaving your computer in sleep mode instead of completely shutting it down. Defragmenting your computer's hard drive may also improve performance, depending on the defragmenting program used. Downloading and installing the latest updates to "The Sims 3" may also help with the problem.
Upgrade Your RAM
If all else fails, your computer's available RAM -- a type of memory -- may just be insufficient for running "The Sims 3" or performing its save functions. Increasing your computer's RAM may be the only answer, especially if you've been trying to play on a computer that doesn't meet the game's minimum requirements. You'll need to purchase compatible memory modules and install them in your computer or have a professional install them for you, depending on your experience with hardware upgrades.
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