Okay, hm. Garry's mod and valve games definitely work fine, so I can't help but feel like there might be a potential conflict. Going to link you our copy & paste text from our chat bot:
Conflicts with Game Capture: Other capture programs, Razer Synapse (disable heatmaps), graphics mods like ENBSeries and SweetFX, and any type of software or utility that displays an in-game overlay like EVGA Precision, MSI Afterburner, TS3/Mumble overlays, Dolby Axon, Raptr, Overwolf, etc. If you use D3DGear it must be uninstalled completely.
So, if you have any of those sort of things active, they could be interfering. This is just a guess based upon the limited information in the log file though. In that log file it says it successfully captured though, which is strange. Maybe an older log? Not entirely sure.
Also, make sure OBS is running as Administrator, that might be needed in some cases.
So basically I'm not entirely sure. If none of these things help come by chat or something and give me a ping and maybe I can take a more direct look at it.