When creating the world everything is fine, no problems.
If i quit out, and then load the world again i crash almost instantly once the world has loaded with this error
java.lang.ArrayIndexOutOfBoundsException: -1

Mod List:

• CD4017BE Library
• The Beneath
• The Erebus
• Vertically Stacked Dimensions

Only seems to happen when using the RCP file and having the add("basicLayer" lines in the RCP file.
When using the ingame editor instead of the RCP i have no issues

ConfigAndError.zip

Your height values were incorrect: the first two numbers in [3, 0, 3, 5]# would mean start noise at y=3 with zero density, increase to full density towards y=0 which is backwards representing a negative bottom noise layer thickness (my code just generated no blocks there). But when you quit and reloaded the game, the -3 turned into a thickness of '253' due to 8-bit clipping in the save format so the generator crashed the game trying to generate blocks blow y=0.

I fixed it so it wouldn't crash anymore but you should still change your heights to [0, 0, 3, 5]# (solid 0 to 3, fade out to 5) or [0, 3, 3, 5]# (fade in from 0 to 3, fade out to 5).