If you get the error message while trying to play content, make sure you have the latest version of your browser. Sometimes it happens that the auto update does not work.
In that case, If you are using Chrome please follow this link: https://support.google.com/chrome/answer/111996?p=fix_chrome_updates&visit_id=637769694165352539-1302859110&rd=1&hl=en-GB
Or the following in case your browser is Firefox: https://support.mozilla.org/en-US/kb/update-failed-error-message-when-updating#w_manual-update
If the issue persists, but you are able to watch trailers, please check these guidelines on how to update CDM module: https://www.remote.tools/remote-work/widevine-content-decryption-module#outdated
After CDM updates, please restart your computer before trying to watch a movie on Rakuten TV.