So this affects objects only, and not the Sims themselves? Is it possible I've eternally messed up that lot now? Hmmm?
Max
As Jordi said, sims are objects too. The only way you've eternally messed up the lot is if you hit delete on any of the error messages. Just resetting all of them shouldn't cause long term problems, although you may end up with 'stuck' off-world objects that don't get deleted because they've lost their reference.
An In-world object is an object on the lot that is visible and you can directly interact with. An out-of-world object still exists on the lot but is invisible. These are mostly controller objects (age controller, pregnancy controller, etc), emitters (like jealously, smells yummy, etc), and placeholders for social interactions.