It crashed when the map is loaded, I only have time to see the settler and the map. It crashed just before you can move. No my mod doesn't use any custom DLL.
Bear with me, since I might repeat a question since it's been a while:
1) Have you tried switching who the host is? There are reports from some people that they can never host civ 5 games without this crash, and in that case switching hosts is a workaround.
2) This also might seem really stupid, but try toggling your graphics and steam settings (enabling/disabling steam overlay, going in and out of fullscreen) etc. for both people.
These are just solutions I see online for a similar problem of that description.