The embedded audio and video codecs might not be compatible with RealPlayer. You can try the following workaround:
1- Install K-Lite from the link below: http://fileforum.betanews.com/download/KLite-Codec-Pack_Full/1094057842/3
Restart the PC and try to convert the file.
Solution 2: Upload the file to Cloud, then download it from Cloud to your PC. Try to convert the downloaded file. Let us know if the file can be uploaded.
Solution 3: Re-install RealPlayer as described here: https://customer.real.com/hc/en-us/articles/204040013-Uninstall-and-reinstall-RealPlayer-on-Windows