I had the SOS screen last night and I did not know to simply press any of the two buttons to fix it, so powered down - I'm now left with a corrupted file.

The camera is obviously capable of fixing the file so does anyone know how to force the camera to repair the file again?

My only other option is £100 commercial app

This might help.
How to fix damaged GoPro HD Hero3 MP4 video with black screen | Sane weblog (http://blog.skrabal.me/how-to-fix-damaged-gopro-hd-hero3-mp4-video-with-black-screen/)

Hi Donald - Yes I tried that and it does work for 50% of the footage but at around £100 it's a bit steep. It's strange that the camera can recognize a corrupted file and fix it (if you press the right button) but there seems to be no way to force it to do it again.