Hmm, that seems like a different issue, then. Check if there may be something like a virus scanner blocking the game from writing files or something.
I just had my first success! The options have saved as has the progress of the completed 1st mission when I went back into the game (with no installation screen).
In addition to your advice, I also had to delete my TD saved games as the RA ones alone didn't work.
I will let you know if I encounter any further problems but sadly looks like I need to redo these missions (I would recommend that anyone having this issue doesn't delete the last savepoint in each mission and see if that works to save the pain of redoing each from start!)
Thanks for your help 🙂
