Describe Crash
Picked up by a Harpy, attacked it, immediately crashed to server menu of all things. Cannot access the world at all even after restarting and reinstalling.

To Reproduce
Get picked up by a harpy?

Crash Log
N/A. Uknown error provides no log, Ctrl+I when prompted does onthing.

Info (please complete the following information):

• Modpack Version: 2.76.1
• Server or Singleplayer: Singleplayer
• Version the world was created on: Survival

Additional context
World was set to LAN when the initial crash occurred. Other worlds function just fine. Occasionally the world will start on a pause menu instead of immediately booting me to the server list, but changing difficulty to Peaceful does nothing. Setting the world to LAN does nothing. Resuming the game results in an immediate crash.

SOLUTION

Installed NBTExplorer, opened the level.dat of the affected world and navigated to my player position line seen here (level.dat>data>player>pos). The first and third positions, X and Z respectively, had somehow been set to NaN; nonexistent values. When the game attempted to use the coordinates to load the player using these value coordinates it would invariably crash. Changing those values to more reasonable number coordinates within NBTExplorer, such as 0, and loading the world gave a real coordinate for the player to load into and solved the problem.