Versions:

MinecraftForge: 14.23.2.2654
Antique Atlas: 4.4.7
Full Modlist

What happens:

Here is the crash log. It's an issue with the world and BiomeID's, and looks related to #159.

I'm having the same issue. This one occurred when I entered a door from the Dimensional Doors mod.
Crash Report.

Antique Atlas 4.4.7
Forge 14.23.3.2655

EDIT: It appears that once #161 is complete, it could fix this.

This should be fixed in 4.4.9