Thanks Dmi3ryd what version of Modo are you using? (I'm using Modo 902 SP3) and I assume you're using the latest test build of the octane plugin. If I simply launch Modo, even before activating Octane, and try to add an Ambient Occlusion render output Modo will crash. Very strange..... I'm was hoping this could be replicated by someone else, will have to do more testing.
Looks like my config file was somehow corrupted. I reverted to an older config file and it now works.
Intel Core i7-4820K, 3x GTX 980ti
Windows 7 64bit, Modo 12.2v2 for PC
Octane build 4.04.0.145