This is the crash report:

---- Minecraft Crash Report ----
// But it works on my machine.

Time: 19/02/14 14.01
Description: Exception in server tick loop

java.lang.NullPointerException: Exception in server tick loop
at com.mojang.authlib.GameProfile.hashCode(GameProfile.java:90)
at java.util.WeakHashMap.hash(Unknown Source)
at java.util.WeakHashMap.put(Unknown Source)
at org.apache.commons.lang3.builder.ToStringStyle.register(ToStringStyle.java:191)
at org.apache.commons.lang3.builder.ToStringStyle.appendClassName(ToStringStyle.java:1453)
at org.apache.commons.lang3.builder.ToStringStyle.appendStart(ToStringStyle.java:378)
at org.apache.commons.lang3.builder.ToStringBuilder.<init>(ToStringBuilder.java:263)
at org.apache.commons.lang3.builder.ToStringBuilder.<init>(ToStringBuilder.java:226)
at com.mojang.authlib.GameProfile.toString(GameProfile.java:97)
at ov.d(SourceFile:102)
at ov.a(SourceFile:93)
at ok.c(SourceFile:130)
at net.minecraft.server.MinecraftServer.v(SourceFile:555)
at nb.v(SourceFile:264)
at net.minecraft.server.MinecraftServer.u(SourceFile:471)
at net.minecraft.server.MinecraftServer.run(SourceFile:387)
at mr.run(SourceFile:657)

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

– System Details –
Details:
Minecraft Version: 14w07a
Operating System: Windows 8 (amd64) version 6.2
Java Version: 1.7.0_51, Oracle Corporation
Java VM Version: Java HotSpot(TM) 64-Bit Server VM (mixed mode), Oracle Corporation
Memory: 962751528 bytes (918 MB) / 1049624576 bytes (1001 MB) up to 2839019520 bytes (2707 MB)
JVM Flags: 0 total;
IntCache: cache: 0, tcache: 0, allocated: 12, tallocated: 94
Profiler Position: N/A (disabled)
Player Count: 2 / 3; [oe['bio1712'/158, l='world', x=219,81, y=58,00, z=172,70], oe['thematbio'/159, l='world', x=227,34, y=70,00, z=168,65]]
Is Modded: Unknown (can't tell)
Type: Dedicated Server (map_server.txt)