Error: "Object reference not set to an instance of an object"

Unable to render RPC Tree in Revit 2019,2020.
The following error is displayed.
Error: “Object reference not set to an instance of an object”

No problem with Revit 2018.

Is there a solution?

Hi,

Here are some questions that will help us investigate the issue:
1. Which version V-Ray for Revit are you using?
2. Does this happen with the native Revit RPCs or you are using Avail ones?
3. Can you make the error occur again and send us the most recent V-Ray for Revit log file located at AppData\Roaming\Chaos Group\V-Ray for Revit 2020\Logs

Best,
Ana