These are the possible reasons you are seeing "Unable to download video" message.
1. Incorrect installation of RealPlayer or older version of RealPlayer.
2. Firewall program is blocking Downloader.
3. Older version of Web browser.
To correct the first reason, please follow the instructions from the below link to resolve your issue.
Please note: If you have any playlists created, you will have to recreate them.
If the issue still persists, please let us know if you have any firewall program installed.