I got this popping up five or six times as the game crashed (attaching screenshot to files, apparently I can't use imgur yet)
1861 June Scenario, no mods, playing as Union. 1.5RC3, as stated in the thread title.
Running Windows 7 SP1 64 bit, 6GB RAM, i7 950, NVIDIA GeForce GTX 660 Ti
Crash occured as I moved to next turn - late September I think. Nothing odd happened during the turn aside from a force railing through Kentucky as a CSA force popped up behind it - I ordered the force to turn around and attack.