Put the summary of the bug you're having here

What I expected to happen was...:
My entire creative mode game would load properly as it has done so many times in the past (i've been building in this particular world for several months)

What actually happened was...:
The game starts loading, returns to the main menu, starts loading again by itself again after a few seconds, and then loads the world. But only a very small portion of the world renders (an area i estimate to be about 50x50 blocks in area), everything else is empty space. The part of the world that remains has not been vertically affected, there are the correct blocks all the way from bedrock to the top of the remains of my structure. when i attempt to fall down into the empty space, my character will fall very slowly down below where the bedrock should be and eventually reappear where he first spawned. I would also like to mention that none of my other worlds on any other mode have encountered any problems like this.
UPDATE: Now when i attempt to load the world, after the "Loading/building terrain" or whatever screen shows, the game will return to the main menu. If i try to load it a second time, the game will freeze on the previously mentioned screen.

Steps to Reproduce:
1. create game in creative mode
2. use the Rohan textue/resource pack downloaded from the Minecraft Middle-Earth website
3. build in world semi-regularly for several months
4. attempt to load world and presto.... sorry, probably not much help.