I am still waiting on that other person to try your fort/boarding save on an AMD machine. But, I did try several times on a Win10 machine, using a standard Intel video chipset and did not have any crash trouble. So your problem is still a mystery because I've been unable to reproduce your colony battle problem on any machine I have access to (Win7 on Intel, WinXP on Intel, Win10 on Intel), even with your save, or other attempts I've made in my own games where I've sacked various towns.