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

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

            {
                let folderPath = strongSelf._folderPathFromFolderName(folderName, insideCacheFolder: true)

                let filePath = (folderPath as NSString).stringByAppendingPathComponent(strongSelf.archiveName)
                let data = NSData(contentsOfFile: filePath)
                completion(data)
            }
