Serveur minecraft

Bonjour,

nous avons créé un serveur minecraft avec un ami sur hamachi. Tout marchait bien jusqu'à ce qu'il m'envoie les fichiers du serveur pour que je l'héberge.
Avant, quand mon ami hébergeait le serveur tout marchait bien on pouvait donc jouer normalement.
maintenant et que quand c'est moi qui lance le serveur avec minecraft server, la console m'affiche sa :
[INFO] Starting minecraft server version Beta 1.7.3
[WARNING] **** NOT ENOUGH RAM!
[WARNING] To start the server with more ram, launch it as "java -Xmx1024M -Xms1024M -jar minecraft_server.jar"
[INFO] Loading properties
[INFO] Starting Minecraft server on *:25565
[WARNING] **** SERVER IS RUNNING IN OFFLINE/INSECURE MODE!
[WARNING] The server will make no attempt to authenticate usernames. Beware.
[WARNING] While this makes the game possible to play without internet access, it also opens up the ability for hackers to connect with any username they choose.
[WARNING] To change this, set "online-mode" to "true" in the server.settings file.
[INFO] Preparing level "findacraft"
[INFO] Preparing start region for level 0
[INFO] Preparing start region for level 1
[INFO] Preparing spawn area: 48%
[INFO] Done (1414367000ns)! For help, type "help" or "?"

Est ce normal ??

Quand j'essaye de me connecter au serveur j'entre soit "localhost" soit mon adresse ip hamachi et la console m'affiche ceci :
[INFO] balpha27072 /127.0.0.1:49458 logged in with entity id 121 at (-51.32181079255806, 82.0, -493.2791924040252)
[SEVERE] Unexpected exception
java.lang.OutOfMemoryError: Java heap space
at fb.a(SourceFile:21)
at fo.b(SourceFile:64)
at iq.a(SourceFile:24)
at fo.b(SourceFile:64)
at iq.a(SourceFile:24)
at fo.b(SourceFile:64)
at ag.a(SourceFile:46)
at hb.a(SourceFile:29)
at he.e(SourceFile:107)
at he.c(SourceFile:60)
at y.<init>(SourceFile:35)
at oo.a(SourceFile:184)
at oo.a(SourceFile:250)
at fc.c(SourceFile:107)
at ee.b(SourceFile:135)
at ee.a(SourceFile:92)
at iv.a(SourceFile:43)
at jl.b(SourceFile:279)
at ee.a(SourceFile:56)
at cu.a(SourceFile:91)
at net.minecraft.server.MinecraftServer.h(SourceFile:378)
at net.minecraft.server.MinecraftServer.run(SourceFile:307)
at bq.run(SourceFile:422)

Aidez mooi s'il vous plais

Merci