I am the developer of my server. Whenever I try and join an arena using the signs I get "Joining Arena 1" but nothing happens. And after clicking it for repeated amounts of times, it says the game is full. When I try the commands "sg join arena 1" and "sg join 1" I get an error, and this is what shows up in the console:
26.03 13:04:17 [Server] SEVERE at net.minecraft.server.v1_5_R2.ThreadServerApplication.run(SourceFile:573)
26.03 13:04:17 [Server] SEVERE at net.minecraft.server.v1_5_R2.MinecraftServer.run(MinecraftServer.java:407)
26.03 13:04:17 [Server] SEVERE at net.minecraft.server.v1_5_R2.MinecraftServer.q(MinecraftServer.java:474)
26.03 13:04:17 [Server] SEVERE at net.minecraft.server.v1_5_R2.DedicatedServer.r(DedicatedServer.java:225)
26.03 13:04:17 [Server] SEVERE at net.minecraft.server.v1_5_R2.MinecraftServer.r(MinecraftServer.java:578)
26.03 13:04:17 [Server] SEVERE at net.minecraft.server.v1_5_R2.DedicatedServerConnection.b(SourceFile:30)
26.03 13:04:17 [Server] SEVERE at net.minecraft.server.v1_5_R2.ServerConnection.b(SourceFile:35)
26.03 13:04:17 [Server] SEVERE at net.minecraft.server.v1_5_R2.PlayerConnection.d(PlayerConnection.java:110)
26.03 13:04:17 [Server] SEVERE at net.minecraft.server.v1_5_R2.NetworkManager.b(NetworkManager.java:292)
26.03 13:04:17 [Server] SEVERE at net.minecraft.server.v1_5_R2.Packet3Chat.handle(Packet3Chat.java:44)
26.03 13:04:17 [Server] SEVERE at net.minecraft.server.v1_5_R2.PlayerConnection.a(PlayerConnection.java:841)
26.03 13:04:17 [Server] SEVERE at net.minecraft.server.v1_5_R2.PlayerConnection.chat(PlayerConnection.java:884)
26.03 13:04:17 [Server] SEVERE at net.minecraft.server.v1_5_R2.PlayerConnection.handleCommand(PlayerConnection.java:966)
26.03 13:04:17 [Server] SEVERE at org.bukkit.craftbukkit.v1_5_R2.CraftServer.dispatchCommand(CraftServer.java:523)
26.03 13:04:17 [Server] SEVERE at org.bukkit.command.SimpleCommandMap.dispatch(SimpleCommandMap.java:187)
26.03 13:04:17 [Server] SEVERE at org.bukkit.command.PluginCommand.execute(PluginCommand.java:44)
26.03 13:04:17 [Server] SEVERE at org.mcsg.survivalgames.CommandHandler.onCommand(CommandHandler.java:156)
26.03 13:04:17 [Server] SEVERE at org.mcsg.survivalgames.commands.Join.onCommand(Join.java:17)
26.03 13:04:17 [Server] SEVERE at org.mcsg.survivalgames.GameManager.addPlayer(GameManager.java:207)
26.03 13:04:17 [Server] SEVERE at org.mcsg.survivalgames.Game.addPlayer(Game.java:175)
26.03 13:04:17 [Server] SEVERE at org.mcsg.survivalgames.SettingsManager.getLobbySpawn(SettingsManager.java:230)
26.03 13:04:17 [Server] SEVERE at org.bukkit.Bukkit.getWorld(Bukkit.java:168)
26.03 13:04:17 [Server] SEVERE at org.bukkit.craftbukkit.v1_5_R2.CraftServer.getWorld(CraftServer.java:818)
26.03 13:04:17 [Server] SEVERE at org.apache.commons.lang.Validate.notNull(Validate.java:203)
26.03 13:04:17 [Server] SEVERE java.lang.IllegalArgumentException: Name cannot be null

If you would like to see for yourself the ip is TeamAstral.mcph.co:25674. I have tried everything within my coding knowledge. I am indeed an amatuer, so tips would be gladly appreciated! I am running the latest development download (0.5.0). I had previously upgraded to the development because it was also not working in the latest release version (0.4.11). We are currently in the setup stage of our server, right now just working out the files, and testing.