whilst loading a world, game randomly crashes ( first time)
shows this report:
---- Minecraft Crash Report ----
// You should try our sister game, Minceraft!

Time: 05/10/13 17:02
Description: Ticking entity

java.lang.OutOfMemoryError: Java heap space
at ej.a(SourceFile:185)
at el.<init>(SourceFile:39)
at jv.l_(SourceFile:166)
at abw.a(SourceFile:1349)
at js.a(SourceFile:479)
at abw.g(SourceFile:1327)
at abw.h(SourceFile:1234)
at js.h(SourceFile:364)
at net.minecraft.server.MinecraftServer.t(SourceFile:471)
at net.minecraft.server.MinecraftServer.s(SourceFile:406)
at bkz.s(SourceFile:124)
at net.minecraft.server.MinecraftServer.run(SourceFile:340)
at hi.run(SourceFile:583)

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

– Head –
Stacktrace:
at ej.a(SourceFile:185)
at el.<init>(SourceFile:39)
at jv.l_(SourceFile:166)
at abw.a(SourceFile:1349)
at js.a(SourceFile:479)
at abw.g(SourceFile:1327)

– Entity being ticked –
Details:
Entity Type: null (jv)
Entity ID: 534702
Entity Name: Mining_Man24
Entity's Exact location: -58.97, 148.81, -416.84
Entity's Block location: World: (-59,148,-417), Chunk: (at 5,9,15 in -4,-27; contains blocks -64,0,-432 to -49,255,-417), Region: (-1,-1; contains chunks -32,-32 to -1,-1, blocks -512,0,-512 to -1,255,-1)
Entity's Momentum: 0.00, 0.00, 0.00
Stacktrace:
at abw.h(SourceFile:1234)
at js.h(SourceFile:364)

– Affected level –
Details:
Level name: Anterna
All players: 1 total; [jv['Mining_Man24'/534702, l='Anterna', x=-58.97, y=148.81, z=-416.84]]
Chunk stats: ServerChunkCache: 1068 Drop: 0
Level seed: 5432869942707136268
Level generator: ID 01 - flat, ver 0. Features enabled: true
Level generator options: 2;7,140x1,5x3,2;3;stronghold,biome_1,decoration,dungeon,mineshaft
Level spawn location: World: (0,4,0), Chunk: (at 0,0,0 in 0,0; contains blocks 0,0,0 to 15,255,15), Region: (0,0; contains chunks 0,0 to 31,31, blocks 0,0,0 to 511,255,511)
Level time: 2331642 game time, 627547 day time
Level dimension: 0
Level storage version: 0x04ABD - Anvil
Level weather: Rain time: 76725 (now: false), thunder time: 151211 (now: false)
Level game mode: Game mode: creative (ID 1). Hardcore: false. Cheats: true
Stacktrace:
at net.minecraft.server.MinecraftServer.t(SourceFile:471)
at net.minecraft.server.MinecraftServer.s(SourceFile:406)
at bkz.s(SourceFile:124)
at net.minecraft.server.MinecraftServer.run(SourceFile:340)
at hi.run(SourceFile:583)

– System Details –
Details:
Minecraft Version: 1.6.4
Operating System: Windows 7 (amd64) version 6.1
Java Version: 1.6.0_31, Sun Microsystems Inc.
Java VM Version: Java HotSpot(TM) 64-Bit Server VM (mixed mode), Sun Microsystems Inc.
Memory: 66487696 bytes (63 MB) / 887816192 bytes (846 MB) up to 954466304 bytes (910 MB)
JVM Flags: 2 total; -XX:HeapDumpPath=MojangTricksIntelDriversForPerformance_javaw.exe_minecraft.exe.heapdump -Xmx1G
AABB Pool Size: 1607 (89992 bytes; 0 MB) allocated, 616 (34496 bytes; 0 MB) used
Suspicious classes: No suspicious classes found.
IntCache: cache: 0, tcache: 0, allocated: 1, tallocated: 63
Profiler Position: N/A (disabled)
Vec3 Pool Size: 122 (6832 bytes; 0 MB) allocated, 81 (4536 bytes; 0 MB) used
Player Count: 1 / 8; [jv['Mining_Man24'/534702, l='Anterna', x=-58.97, y=148.81, z=-416.84]]
Type: Integrated Server (map_client.txt)
Is Modded: Probably not. Jar signature remains and both client + server brands are untouched.