The Sketchup Octane Exporter works just fine in SUp v8... IF it's properly installed.
I suggest you remove the 'octane loader' .rb file
and the whole Octane sub-folder in Plugins.
Check for other rogue files in the wrong folders and remove them too - look through the files in the main zip-file to see what files/sub-folders should be where...
Then make a completely fresh install following the instructions...
Extracting the files/sub-folders with files etc
exactly as they appear in the zipped file.
If the problem persists please open the Ruby Console, try to run the Octane Exporter and see any error messages, post error messages here as these will help track down your problem.....