Minecraft crashing when I enter a certain world?

[Duinis]

Minecraft crashes when I enter my creative world. For all the others it's ok.

Here's the crash report thingummy.
---- Minecraft Crash Report ----
// I blame Dinnerbone.

Time: 23/09/13 6:39 AM
Description: Rendering screen

java.lang.RuntimeException: Failed to check session lock, aborting
   at alq.h(SourceFile:44)
   at alq.<init>(SourceFile:30)
   at alm.<init>(SourceFile:16)
   at aln.a(SourceFile:83)
   at atv.a(SourceFile:1417)
   at awh.e(SourceFile:157)
   at awi.a(SourceFile:210)
   at awg.a(SourceFile:173)
   at awh.a(SourceFile:183)
   at bfe.b(SourceFile:718)
   at atv.S(SourceFile:686)
   at atv.d(SourceFile:619)
   at net.minecraft.client.main.Main.main(SourceFile:101)


A detailed walkthrough of the error, its code path and all known details is as follows:
---------------------------------------------------------------------------------------

-- Head --
Stacktrace:
   at alq.h(SourceFile:44)
   at alq.<init>(SourceFile:30)
   at alm.<init>(SourceFile:16)
   at aln.a(SourceFile:83)
   at atv.a(SourceFile:1417)
   at awh.e(SourceFile:157)
   at awi.a(SourceFile:210)
   at awg.a(SourceFile:173)
   at awh.a(SourceFile:183)

-- Screen render details --
Details:
   Screen name: blt
   Mouse location: Scaled: (302, 203). Absolute: (605, 299)
   Screen size: Scaled: (683, 353). Absolute: (1366, 706). Scale factor of 2
Stacktrace:
   at bfe.b(SourceFile:718)
   at atv.S(SourceFile:686)
   at atv.d(SourceFile:619)
   at net.minecraft.client.main.Main.main(SourceFile:101)

Someone help me out please? Thanks.

[☣2crzy4uall☣]

you can try and delete the session.lock file from your world folder.

the location of your saves is "%appdata%\.minecraft\saves"
go in to the folder of the save that give you trouble and delete the session.lock file.

[gavin1928374655]

load it up in MCEDIT and 'save' the file.

that fixed an error with one of my worlds, i somehow corrupted it. resaving it fixed the problem

[Duinis]

Fixed it, turns out I actually made my world file "Hidden" xD