I have had this happen periodically in the last few days. I have not used Octane in several weeks, and it was very frustrating. I launched the standalone to confirm that my license info was good (it was.) I left standalone running when I re-launched Cinema and tried using Octane again. I received that same error. I made to sure to get all of the current versions of both standalone and the plug in. At some point, even though the error screen appeared, Octane did load, and I could use it.
After reading this post, I decided to try again today, and sure enough, the same thing: first an error, then the UI appeared. Here is the snippet from the Console window:
It seems as if there is some communications thing not being initialized at first.
The error dialog closed before I could grab a screenshot. The Devices tab shows all of my GPUs as I would expect.
Hope this helps, Ahmet!
CaseLabs Mercury S8 / ASUS Z10PE-D8 WS / Crucial 64GB 2133 DDR4 / 2 XEON E5-2687W v3 3.1 GHz / EVGA 1600 P2 / 2 EVGA RTX 2080Ti FTW3 Hybrid/ Cinema 4D
Is it fast? Oh, yeah!