player does not enter neather wile in minecart

if player is in a minecart goes into neather portal neather goes into neather until player gets out minecart then minecart diapears into neather portal but not player plus i had several crahses wihile trying.

Minecraft Crash Report ----
// I feel sad now 😞

Time: 7/13/13 11:35 PM
Description: Sending packet

java.lang.NullPointerException
at cm.b(SourceFile:116)
at cm.a(SourceFile:41)
at jz.b(SourceFile:421)
at hm.b(SourceFile:648)
at hm.a(SourceFile:82)
at bkz.b(SourceFile:73)
at net.minecraft.server.MinecraftServer.t(SourceFile:488)
at net.minecraft.server.MinecraftServer.s(SourceFile:405)
at bkw.s(SourceFile:124)
at net.minecraft.server.MinecraftServer.run(SourceFile:339)
at hh.run(SourceFile:582)

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

– Head –
Stacktrace:
at cm.b(SourceFile:116)
at cm.a(SourceFile:41)

– Packet being sent –
Details:
Packet ID: 4
Packet class: fw
Stacktrace:
at jz.b(SourceFile:421)
at hm.b(SourceFile:648)
at hm.a(SourceFile:82)
at bkz.b(SourceFile:73)
at net.minecraft.server.MinecraftServer.t(SourceFile:488)
at net.minecraft.server.MinecraftServer.s(SourceFile:405)
at bkw.s(SourceFile:124)
at net.minecraft.server.MinecraftServer.run(SourceFile:339)
at hh.run(SourceFile:582)

– System Details –
Details:
Minecraft Version: 1.6.2
Operating System: Windows XP (x86) version 5.1
Java Version: 1.7.0_21, Oracle Corporation
Java VM Version: Java HotSpot(TM) Client VM (mixed mode, sharing), Oracle Corporation
Memory: 31815160 bytes (30 MB) / 244342784 bytes (233 MB) up to 518979584 bytes (494 MB)
JVM Flags: 1 total; -Xmx512M
AABB Pool Size: 36530 (2045680 bytes; 1 MB) allocated, 36530 (2045680 bytes; 1 MB) used
Suspicious classes: No suspicious classes found.
IntCache: cache: 0, tcache: 1, allocated: 3, tallocated: 69
Profiler Position: N/A (disabled)
Vec3 Pool Size: 5246 (293776 bytes; 0 MB) allocated, 5246 (293776 bytes; 0 MB) used
Player Count: 0 / 8; []
Type: Integrated Server (map_client.txt)
Is Modded: Probably not. Jar signature remains and both client + server brands are untouched.

Minecraft Crash Report ----
// I feel sad now 😞

Time: 7/13/13 11:35 PM
Description: Sending packet

java.lang.NullPointerException
at cm.b(SourceFile:116)
at cm.a(SourceFile:41)
at jz.b(SourceFile:421)
at hm.b(SourceFile:648)
at hm.a(SourceFile:82)
at bkz.b(SourceFile:73)
at net.minecraft.server.MinecraftServer.t(SourceFile:488)
at net.minecraft.server.MinecraftServer.s(SourceFile:405)
at bkw.s(SourceFile:124)
at net.minecraft.server.MinecraftServer.run(SourceFile:339)
at hh.run(SourceFile:582)

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

– Head –
Stacktrace:
at cm.b(SourceFile:116)
at cm.a(SourceFile:41)

– Packet being sent –
Details:
Packet ID: 4
Packet class: fw
Stacktrace:
at jz.b(SourceFile:421)
at hm.b(SourceFile:648)
at hm.a(SourceFile:82)
at bkz.b(SourceFile:73)
at net.minecraft.server.MinecraftServer.t(SourceFile:488)
at net.minecraft.server.MinecraftServer.s(SourceFile:405)
at bkw.s(SourceFile:124)
at net.minecraft.server.MinecraftServer.run(SourceFile:339)
at hh.run(SourceFile:582)

– System Details –
Details:
Minecraft Version: 1.6.2
Operating System: Windows XP (x86) version 5.1
Java Version: 1.7.0_21, Oracle Corporation
Java VM Version: Java HotSpot(TM) Client VM (mixed mode, sharing), Oracle Corporation
Memory: 31815160 bytes (30 MB) / 244342784 bytes (233 MB) up to 518979584 bytes (494 MB)
JVM Flags: 1 total; -Xmx512M
AABB Pool Size: 36530 (2045680 bytes; 1 MB) allocated, 36530 (2045680 bytes; 1 MB) used
Suspicious classes: No suspicious classes found.
IntCache: cache: 0, tcache: 1, allocated: 3, tallocated: 69
Profiler Position: N/A (disabled)
Vec3 Pool Size: 5246 (293776 bytes; 0 MB) allocated, 5246 (293776 bytes; 0 MB) used
Player Count: 0 / 8; []
Type: Integrated Server (map_client.txt)
Is Modded: Probably not. Jar signature remains and both client + server brands are untouched.