I don't see a cause but there is a lot of log activity, you could try starting KSP with " -nolog" to see if it helps. You can add the line to a shortcut properties or to the Steam custom launch box.
Hmm, can you please try clearing the assignment and then pressing space and changing the lit options, this may be a Windows issue as I was able to redefine on Linux.
If the download failed you'll need to verify the game cache to make it download any missing or damaged files, this should be standard procedure for anyone on Steam