Yep, this seems to be fixed. Ta.

I seem to have resolved the problem by simply removing the affected scenario folder from the Arma 3 Missions folder and replacing it with a backup I created recently. Luckily I didn't lose a heap of work as the backup is fairly up to date. .. It does seem a little strange that 1 bad scenario out of 14 could make the whole thing crash but I'm happy that the solution was fairly painless. I will leave this ticket open for a day or so just to make sure the problem really is solved. .. Cheers.