Swift creating NSError Object

Looks like you want (see dictionary keys):

Swift 2

let userInfo: [NSObject : AnyObject] =
[
    NSLocalizedDescriptionKey :  NSLocalizedString("Unauthorized", value: "Please activate your account", comment: ""),
    NSLocalizedFailureReasonErrorKey : NSLocalizedString("Unauthorized", value: "Account not activated", comment: "")
]

Swift 3

let userInfo: [AnyHashable : Any] =
            [
                NSLocalizedDescriptionKey :  NSLocalizedString("Unauthorized", value: "Please activate your account", comment: "") ,
                NSLocalizedFailureReasonErrorKey : NSLocalizedString("Unauthorized", value: "Account not activated", comment: "")
        ]

Then create the error object in both swift 2 or 3 like this:

let err = NSError(domain: "ShiploopHttpResponseErrorDomain", code: 401, userInfo: userInfo)
println("Error in Post: \(err.localizedDescription)")

NSLocalizedDescriptionKey and NSLocalizedFailureReasonErrorKey are global String variables, and the keys inside of the userInfo dictionary. The values are slightly different from what you specified:

println(NSLocalizedDescriptionKey) //prints "NSLocalizedDescription"
println(NSLocalizedFailureReasonErrorKey) //prints "NSLocalizedFailureReason"

I find it good practice to look at the documentation by right-clicking the class (NSError in this case) and selecting "Jump To Definition" within xcode. All kinds of questions can be answered this way. :)

Creating a very simple error in Swift 3:

let error = NSError(domain: "", code: 0, userInfo: [NSLocalizedDescriptionKey : "Object does not exist"])

Creating an error is as simple as following line:

let error = NSError(domain: "com.example.error", code: 0, userInfo: [NSLocalizedDescriptionKey: "message"])

If you need additional stack trace information, use following method:

func error(_ message: String, code: Int = 0, domain: String = "com.example.error", function: String = #function, file: String = #file, line: Int = #line) -> NSError {

    let functionKey = "\(domain).function"
    let fileKey = "\(domain).file"
    let lineKey = "\(domain).line"

    let error = NSError(domain: domain, code: code, userInfo: [
        NSLocalizedDescriptionKey: message,
        functionKey: function,
        fileKey: file,
        lineKey: line
    ])

    // Crashlytics.sharedInstance().recordError(error)

    return error
}

Usage:

let localizedErrorMessage: String = NSLocalizedString("Unauthorized", comment: "Account not activated")
let error = error(localizedErrorMessage)