It appears that one of the 2 things are causing this problem.
- Bad installation of RealPlayer.
- Your Windows is missing certain codecs.
To make sure installation issue is taken care of, 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.
To make sure your Windows is not missing any codecs, here are some tips.
Installing the K-Lite codec pack often helps to fix issues related to playback. You can install it from the link below:
After installing the codec, restart your computer and try playing the videos again.
Lastly, please make sure you have all of your Windows updates installed.
Please let us know if the issue persists.