To resolve this issue, I would recommend you install the k-lite codec pack:
If that doesn't help, try uninstalling reinstall the RealPlayer Cloud by following the steps in this article:
You can then download RealPlayer Cloud from this link:
Sign in to access the plus features. To do so, follow steps in this article:
In order to play DVD, check on this link: https://customer.real.com/hc/en-us/articles/204041203
Note: When you purchase RealPlayer Plus 16, we've provided 10 days for a refund if you are not satisfied with the product. As it has been few years since you purchase, we are unable to honor the refund.