We don't offer support in Korean.
Please follow these instructions to resolve your downloader issue.
1. Type Internet Options in the Windows search bar or open Internet Explorer and click Internet Options.
2. Under Browsing History, click Delete and Delete again when prompted.
3. Click OK and close Internet Options/Internet Explorer.
4. Open one of the web browsers (Google Chrome, Mozilla Firefox, Microsoft Edge) and go to YouTube.com.
5. Click the Download This Video button. (You will still receive no titles at this time)
6. Close all Windows and restart your PC.
7. Go back to your web browser and download a video.