Well, I finally got it working. I had to install manually and I also had to select Octane as renderer otherwise it would not load.

Today I downloaded Octane 4 for rhino 5 and 6.
Installation for rhino 5 was OK but for Rhino 6 I get the same faults as Tipperz. I tried to do the same thing as he did but I can't get it to work. I use Rhino 6.10 and Win 7.