RavenDeath18 As a test, please try playing in a clean user folder. Move the entire Sims 3 folder out of Documents > Electronic Arts and onto your desktop. When you launch the game, a clean folder will spawn with no content. (Your saves and other content will be intact in the folder you've moved but temporarily unread by the game.) Don't add anything to the new folder yet; just see whether you can select and load a new save.
If that doesn't work, please post a screenshot of the error you're getting. I don't think I've seen it before, but maybe I'm not understanding what you're seeing.