Custom Modpack Crash

[currylambchop]

[currylambchop]

Solved.

[plowmanplow]

For the curious, and to help folks who find this on a Google search, this was a Potion ID conflict at ID 31. Potion ID conflicts are uncommon, but they can happen just like conflicts for items, blocks, enchantments, biomes, etc. The error message above (which should have been in spoiler tags):

java.lang.IllegalArgumentException: Overwriting already-registered Potion assets.borderlands.PotionShock@73181de6 @ 31

shows that another mod is trying to overwrite a Borderlands mod's potion. An easy way to fix this would be to temporarily disable the Borderlands mod and start the client. Use NEI to dump a list of potion IDs and examine that list to see which mod is already using ID 31. This will give you enough information to be able to change the ID in one of the two conflicting mods.