Error while running launchMinecraft(): java.lang.NullPointer ....... please help me
Isn't this an error from trying to run Java8? Try Java7 - 64bit and see if you get the same error.
Unrelated...and this might get a little wordy...
This pack introduced me to EnderIO, so I'm unfamiliar with how the Powered Spawners function [aside from what I was able to read on the wiki]. The one issue I see specific to this pack, with regards to EIO's spawner, is unwanted mobs in an Enderman spawn chamber. Enderman spawner requires low-light levels to function. The only mob transport method that still prevents teleporting [aside from minecarts] is XU's Conveyor Belt. XU's belt allows mob spawning. So if you setup an Enderman spawner, you're going to get unwanted mobs in that system.
Hopefully I'm missing something. I'm assuming EIO's spawner uses vanilla spawner mechanics [player near, light levels] and adds the additional requirement of the block being powered. Am I wrong in that assumption? Does EIO substitute the vanilla conditions for spawners with just the power requirement?
The only other solution I see is to not funnel Endermen to a central killzone, but to line the spawn room floor with Punji sticks/Iron Spikes and have Vacuum Chests in the walls collecting drops.
Edit: limited testing revealed that perhaps EIO does remove light-level restrictions for spawn conditions. Testing chamber had enough glowstone to completely light the chamber floor [as well as a good potion of the interior] and I was still getting 3 Endermen per spawn cycle. Also, the problem I described above only presents itself when you move away from the spawner [so random mobs are able to spawn within the chamber].