I’m not sure what has happened but if you haven’t been able to fix it the Sims 3 folder may have become corrupted. You could fix it by renaming the existing folder. Then launch the game. It’ll make a fresh Sims 3 folder. Then reinstall your content including the problem world. Once you are happy with the new folder you can put your save file into the new Saves folder and test to see if you can launch the game.
You can keep a backup copy of any build or household by going into edit town and evict the sims to the clipboard then click them and choose the share option. Sharing will save them to the Exports folder as a Sims3Pack file. This file can be installed into any Sims 3 folder using the launcher.
