Do you have the object(s) to be instanced enabled? Currently, the plugin can't instance objects that are not enabled in the scene. If you need to hide these master objects from the rendering, you have an option in the Octane spare parameters to hide them, but they must be enabled or the plugin is not going to be able to extract them.
In any case, the plugin should never crash. I'll try to reproduce this problem here, but can you please attach your scene to be sure that I'm testing the same problem?
Computer Graphics Software Developer
Octane plugin development and support: LightWave and Houdini