That's what I did (just stuck the whole plate in the dishwasher) and it fixes the can't eat problem for the moment, but it is a recurring bug in my game. The first time it happened was with the caprese salad when one of my active sims was a toddler. It didn't recur until today with the garden salad. It happened to a different sim in the same active family and they are now teens. Both times I got rid of all the food and sold the refrigerator. I also have a problem with that family where no one can complete a violin or piano song, which has never happened before. They just continue to compose it forever and the action never completes (even after 12 sim hours). I may have to do the cache delete thing since I already tried repairing the game twice (after each time it happened) and I'm still having problems.