I had the same problem a few days ago and I suggest you to perform a fresh installation of the software. Therefore, go to Control Panel > Uninstall a program > search Video Download Converter and hit uninstall. After that a good idea is to download again the setup file, but this time be sure that you download the latest version. You can start the download process by pressing the Free Download button from its official webpage. After the download is complete, open the setup file and start the installation process once again.
If you still have the same problem after you pass all these steps, I recommend you to try another YouTube video Downloader like Xilisoft Download YouTube Video