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 .
Yes, everybody has this issue now with Radeon Render at least on Mac. Go back to the beta version released on May 15th and you will be ok for now.
How do I get that version of Blender 2.8? I couldn't find it
I assume you do not have Time Machine that holds earlier versions? That is how I got mine back.
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.
https://community.amd.com/docs/DOC-2183?sr=stream this should work.
This is much appreciated...
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