Hey, I actually figured this one out! Using a debugger to skip past the bad memory access I got a message from the Altarians:
"Your war against the <space> has no merit." We declare war on you, yada yada.
What happened is I made peace with the Korx -- who I declared war on as a favor to a minor race they were about to annihilate -- anyway, I made peace with the Korx on this very turn. The Altarians' null causus belli is crashing the system!