@SharkyBruce Okay, since I don't know what you've tried already, I'll list a couple of steps that might help.
Delete the five cache files in your game folder in Documents. While troubleshooting, delete them every time you quit the game, even if it didn't help before. These files (CASPartCache, compositorCache, scriptCache, simCompositorCache, and socialCache) will fill with stale or corrupt data, so keep trashing them.
If that doesn't work, pull your entire TS3 game folder out of Documents and onto your desktop. Launch the game to spawn a new game folder (no need to go past the Main Menu), then quit. Copy over your Saves folder from the old game folder to the new one. If the save uses a store or custom world, also copy over the contents of DCCache and InstalledWorlds, but otherwise, leave everything else out of the new game folder. You might get a warning about missing objects, but that's fine, you're not going to save your progress—the point is to see if the save will load at all.
If this doesn't help either, you might need to load a backup version of the save. Even if you never make any, the game keeps the files from the second to last time you saved. So trash the new game folder you created above, and make a new one. Go into your old game folder, into Saves, and find the folder that has the name of your borked save but with a .backup extension. (So if your save is called SunsetValley, your existing save folder will be SunsetValley.sims3, and your backup will be SunsetValley.sims3.backup.) Delete the .backup extension and rename that save folder (i.e. SunsetValley1.sims3), and transfer it into your new game folder.
If none of this helps, there's one more long shot technique to try, but otherwise, the save might not be recoverable.
