Looking at the source I'm not sure how this could happen, but it's crashing every time I try to load the world for me.

crash-2016-08-26_09.07.54-server.txt

a mod's machine or something is returning true from hasCapability but null from getCapability
<.<
https://github.com/williewillus/Botania/blob/master/src/main/java/vazkii/botania/common/item/equipment/bauble/ItemItemFinder.java#L174

Are you playing on a modpack I can readily install?

If so I could get your world and do more extensive debugging

All The Mods. I can send it to you.

Awesome, throw it up somewhere and i'll take a look

Sent privately (don't want to overwhelm my dropbox).

It's an IE tile entity being finicky, Refer IE ticket ^

For now if anyone has a "Spectator" bauble equipped you can edit it out of their Bauble inventory with an NBT editor to unbreak the save