Put the summary of the bug you're having here

What I expected to happen was...:
Existing world to appear and to continue playing the game

What actually happened was...:
world starts to load then shortly after comes up with a game output tab with the following script:

Steps to Reproduce:
1. open up the minecraft launcher 1.6.11
2. ...Click on Play
3. ...Click on single player
4. Click on the relevant world and selected the world
5. following script comes up
[Client thread/INFO]: Setting user: egg_653a
[08:17:19] [Client thread/INFO]: (Session ID is token:453b98ab82ec48ddb68b5914a27feb65:da49946fca694ab1ad8573396474d051)
[08:17:21] [Client thread/INFO]: LWJGL Version: 2.9.1
[08:17:22] [Client thread/INFO]: Reloading ResourceManager: Default
[08:17:23] [Sound Library Loader/INFO]: Starting up SoundSystem...
[08:17:23] [Thread-6/INFO]: Initializing LWJGL OpenAL
[08:17:23] [Thread-6/INFO]: (The LWJGL binding of OpenAL. For more information, see http://www.lwjgl.org)
[08:17:23] [Thread-6/INFO]: OpenAL initialized.
[08:17:23] [Sound Library Loader/INFO]: Sound engine started
[08:17:26] [Client thread/INFO]: Created: 512x512 textures-atlas
[08:17:32] [Server thread/INFO]: Starting integrated minecraft server version 1.8.1
[08:17:32] [Server thread/INFO]: Generating keypair
[08:17:32] [Server thread/INFO]: Preparing start region for level 0
[08:17:33] [Server thread/INFO]: Preparing spawn area: 39%
[08:17:34] [Server thread/INFO]: Changing view distance to 12, from 10
[08:17:35] [Server thread/INFO]: egg_653a[local:E:6cb2e606] logged in with entity id 322 at (287.0248862703696, 93.1143565909306, 401.5398141659949)
[08:17:35] [Server thread/INFO]: egg_653a joined the game
[08:17:38] [Server thread/WARN]: Can't keep up! Did the system time change, or is the server overloaded? Running 2200ms behind, skipping 44 tick(s)

Followed by
[08:30:57] [Client thread/INFO]: Setting user: egg_653a
[08:30:57] [Client thread/INFO]: (Session ID is token:453b98ab82ec48ddb68b5914a27feb65:da49946fca694ab1ad8573396474d051)
[08:31:00] [Client thread/INFO]: LWJGL Version: 2.9.1
[08:31:01] [Client thread/INFO]: Reloading ResourceManager: Default
[08:31:01] [Sound Library Loader/INFO]: Starting up SoundSystem...
[08:31:02] [Thread-6/INFO]: Initializing LWJGL OpenAL
[08:31:02] [Thread-6/INFO]: (The LWJGL binding of OpenAL. For more information, see http://www.lwjgl.org)
[08:31:02] [Thread-6/INFO]: OpenAL initialized.
[08:31:02] [Sound Library Loader/INFO]: Sound engine started
[08:31:05] [Client thread/INFO]: Created: 512x512 textures-atlas
[08:31:43] [Server thread/INFO]: Starting integrated minecraft server version 1.8.1
[08:31:43] [Server thread/INFO]: Generating keypair
[08:31:44] [Server thread/INFO]: Preparing start region for level 0
[08:31:45] [Server thread/INFO]: Preparing spawn area: 11%
[08:31:46] [Server thread/INFO]: Preparing spawn area: 54%
[08:31:47] [Server thread/INFO]: Changing view distance to 12, from 10
[08:31:47] [Server thread/INFO]: egg_653a[local:E:da01223c] logged in with entity id 336 at (284.70693432027974, 93.1143565909306, 364.5939638990032)
[08:31:47] [Server thread/INFO]: egg_653a joined the game
[08:31:49] [Server thread/INFO]: Saving and pausing game...
[08:31:49] [Server thread/INFO]: Saving chunks for level 'ronnies survival'/Overworld
[08:31:50] [Server thread/INFO]: Saving chunks for level 'ronnies survival'/Nether
[08:31:50] [Server thread/INFO]: Saving chunks for level 'ronnies survival'/The End
#

1. A fatal error has been detected by the Java Runtime Environment:
   #
2. EXCEPTION_ACCESS_VIOLATION (0xc0000005) at pc=0x000000001b5ba9b5, pid=6196, tid=8272
   #
3. JRE version: Java(TM) SE Runtime Environment (8.0_25-b18) (build 1.8.0_25-b18)
4. Java VM: Java HotSpot(TM) 64-Bit Server VM (25.25-b02 mixed mode windows-amd64 compressed oops)
5. Problematic frame:
6. C [ig75icd64.dll+0x6a9b5]
   #
7. Failed to write core dump. Minidumps are not enabled by default on client versions of Windows
   #
8. An error report file with more information is saved as:
9. C:\Users\The\AppData\Roaming\.minecraft\hs_err_pid6196.log
   #
10. If you would like to submit a bug report, please visit:
11. http://bugreport.sun.com/bugreport/crash.jsp
12. The crash happened outside the Java Virtual Machine in native code.
13. See problematic frame for where to report the bug.
    #
    AL lib: (EE) alc_cleanup: 1 device not closed
    Java HotSpot(TM) 64-Bit Server VM warning: Using incremental CMS is deprecated and will likely be removed in a future release