             {
                 let folderPath = strongSelf._folderPathFromFolderName(folderName, insideCacheFolder: true)
 
-                let filePath = folderPath.stringByAppendingPathComponent(strongSelf.archiveName)
+                let filePath = (folderPath as NSString).stringByAppendingPathComponent(strongSelf.archiveName)
                 let data = NSData(contentsOfFile: filePath)
                 completion(data)
             }

    private func _deleteCache() {
        let folderName = name
        let folderPath = _folderPathFromFolderName(folderName, insideCacheFolder: true)
        let filePath = folderPath.stringByAppendingPathComponent(archiveName)
        do {
            try NSFileManager.defaultManager().removeItemAtPath(filePath)
        }

                print(folderPath)
                strongSelf._createFolderIfNeeded(folderPath)
                
                let filePath = (folderPath as NSString).stringByAppendingPathComponent(strongSelf.archiveName)
                
                data.writeToFile(filePath, atomically: true)
                if strongSelf.saveOperationQueue.operationCount == 1 {
