I probably have not explained correctly. We are unable to select the material in the light which is the Default Light Source. In the attached image the default light source material is the underside of the linear fitting. We had an IES file attached and it initially worked. When we opened another view we received the message.
The Octane Material default is stored as an OCS file (ie. Octane scene) when you select Save as Default for a given material. It looks like in this case the "Default Light Source.OCS" file has become corrupt - so when loaded the default Octane material for the Revit Default Light Source material this error is being given. Would it be possible pls to send me the
C:\Users\[username]\AppData\Local\OctaneRender for Revit\Defaults\Default Light Source.ocs file? After sending it to me - you can delete that file, and your scene should load correctly (but your custom Octane node setup for that material will be lost).
Paul