You're working on your app. Everything seems fine. Then boom! You get a scary message like NSCocoaErrorDomain error 4 or error 3840 . If that made your heart skip a beat—you’re not alone. These errors are common in iOS and macOS apps. They usually show up when the system runs into trouble with files, data, or permissions. But let’s break it down. The word “Cocoa” refers to Apple’s development environment. The NSCocoaErrorDomain is just Apple’s way of saying something didn’t go as planned. Maybe the app couldn't find a file. Maybe it couldn't read or write data. Or maybe your JSON was just a little messy. Don’t worry—these errors are not a sign of failure. They are helpful warnings. They show you exactly where things went off track. Better yet? Most of them are super easy to fix. In this guide, we’ll walk through common causes and quick fixes for NSCocoaError issues. You’ll get smart solutions that even a beginner can use. So take a breath. You don’t need to be a co...