I get this error on a Blender 2.8 Beta which had a build date of today. This is a clean install and I have not messed with any of the files so I have no idea if this error is replicable .
While this version of RPR and Blender do not like each other, there is a new version coming very soon that will fix this issue. The issue is that the Blender Plug-in API received some massive changes and as a result most plugins are currently broken. Feature freeze has happened for 2.8 though so the fix is almost here.