I'm attempting to reinstall Sky Demon on my Windows 8 PC after it locked up irretrievably and have to be wiped and rebuilt. When I get to the stage where I'm asked for my login and password, I get the following message: 'Failed to write the licence file to disk. Please check that the file below is not write-protected and try again'. As the installer has clearly just written that file it seemed unlikely to me that it could be write-protected, and so it transpired: no write protect. So what gives?

The installer does not write that file. I really can't give you any more information than the error message itself is giving you. Something on your system is stopping SkyDemon from writing that file, which is your SkyDemon license. Just delete the file yourself, and all should be well.