Coto

Notice that I turned off read-only, I didn't turn it on Many people were having these problems after a re-install, I guess some files are created as read-only during install. I believe that under certain (maybe localization related?) circumstances Steam bugs out when it cannot access these files, and this causes the problem.

This is certainly not a new thread, but it is the top search result on Google for this problem so I thought I would chime in with what solved this for me. After trying so many things and even having the same problem on a completely new PC and OS install: Check the KSP-folder, make sure nothing is set to read-only (check the top-level folder). The game launches fine from Steam after removing read-only, at least for me. Hopefully this helps someone!