I've bound an NSDatePicker to a date attribute in one of my Core Data entities via an NSArrayController. This causes the following errors in the debugger console whenever the value is triggered: Code: 2008-01-13 10:24:42.360 Ziggy[14788:10b] Error setting value for key path selection.lastActivity of object <NSArrayController: 0x139280>[entity: IOControllers, number of selected objects: 1] (from bound object <NSDatePicker: 0x12fd50> with object ID 404 in Nib named MainMenu.nib): [<NSManagedObject 0x1e0460> setValue:forUndefinedKey:]: the entity IOControllers is not key value coding-compliant for the key lastActivity. All my other attributes work just fine, it's only the date attribute that's failing but I can't for the life of me work out why. I've even resorted to Apple's own Core Data videos, which cover using a date attribute with an NSDatePicker, but other than all of Apple's documentation still covering Xcode 2.x instead of 3.0 they don't do anything different to what I have. I'm using Xcode 3 and Leopard - has something changed that is breaking this?