The following error occurs when the server starts:
It appears to be caused by the Ender Storage mod failing to load in the contents of Ender Storage containers in the Deep Dark (DIM-100). It is unclear if this always happens or if it is triggered by certain item ids being present. Ender Storage contents are saved in:
Editing this file using NBTExplorer and removing all the entries will let the server start again. However, this will remove all items from Ender Storage.