Wait a minute, if Minecraft crashes everytime he spawns, then how did you get him to spawn there? 
I take it that that's a mod, right?
It only crashes when he spawns. After he's spawned, I can run Minecraft again on the same world and he'll be there, and nothing crashes until another spawns.
Also, no, it isn't a mod! That's the amazing part of this map: No mods required!
How I did it:
I've put how I did it into a spoiler since it's a long explanation and I don't want to spam up this thread. First, I went into Minecraft and placed 3 chests: One with a Diamond Chestplate, Leggings, and Boots. The second with a Diamond Pickaxe, and the third with a normal player head. After that, I saved Minecraft and quit, and ran the world in MCedit. Then, in MCedit, I had run SethBling's 'player skulls' filter (which allows me to create the head of any player, using their skin) on the chest with the player head, and had changed it into Herobrine's Head. Then I had used a filter on the chest with a pickaxe to enchant it with Sharpness V and Knockback III. Finally, I ran the same filter on the chest with armor, and gave it all forms of Protection III and Unbreaking III.
Next, I went into Minecraft again. I took the items out of their chests, and created one new chest where I wanted my Herobrine spawner to be. I placed the items into the new chest, closed the chest, then closed Minecraft. I went into MCedit again and ran another one of SethBling's filters: CreateGearedMobs, which allows me to make a monster with the items in the chest equipped.
As of now, we have a zombie with Herobrine's Head, Diamond Armor, and a Pickaxe.
After that, I gave the zombie the Speed III potion effect with the time set to 3,000,000 seconds. Then, finally, I used another one of SethBling's filters, CreateMobSpawners to turn the zombie into a Monster Spawner, and used another filter to set the Monster Spawner to spawn one monster every 7 - 10 minutes.
Anyway, I think I've found the reason it crashed. However, it isn't something I can fix. It's related to Herobrine's head, meaning I'll need to make a new boss. :C Sorry, guys. Herobrine most likely won't be in the map.