It seems that Houdini can't load the plugin. The problem can be related to several issues:
1) Do you know if Octane Standalone works fine on this system? If it works the problem is on the Houdini plugin side for sure.
2) Check the houdini.env file configuration. The HOUDINI_PATH variable plugin build should match the Houdini build that you are using. To be sure, you can attach your houdini.env file here to check it.
3) Can you please check if you get an error reported in the console while launching Houdini? Open a console and start Houdini from it to see if an error related to the plugin is reported. Perhaps a needed lib is missing. For example, I've found that several new Linux distributions don't have the needed freeglut lib installed by default.
Computer Graphics Software Developer
Octane plugin development and support: LightWave and Houdini