core-data error question

A store is basically another term for an actual Core Data database. A model is kind of like the format or design of the database, based on the entities and relationships that you define. When the store is initially created, it will be based on whatever model it is meant for. Your app uses the model to figure out how to read a store created with that model. If you change the model and then try to use it to open a store based on an older version of the model (without letting Core Data do any kind of migration), you will get that error.

You can delete your app from the simulator/device in order for the store to be deleted as well, and then it will be re-created using the newer version of the model the next time you run the app. Of course, you will lose any data that had been in the old store.