I only have one person that can't connect. Here's the error from the log.
Spoiler
12.06 12:24:52 [Server] INFO [Minecraft-Server] Saved the world12.06 12:24:52 [Server] INFO [Minecraft-Server] Saving…
12.06 12:24:52 [Server] INFO [Minecraft-Server] Turned on world auto-saving
12.06 12:24:52 [Multicraft] Auto-saving world…
12.06 12:23:38 [Disconnect] User [Minecraft-Server] nutcase84 has disconnected, reason: disconnect.quitting
12.06 12:23:15 [Server] INFO [Minecraft-Server] nutcase84 fell out of the world
12.06 12:23:11 [Server] INFO [Minecraft-Server] [nutcase84: Teleported nutcase84 to 255.50,-254.50,255.50]
12.06 12:21:32 [Server] INFO [Minecraft-Server] [nutcase84: Teleported nutcase84 to 255.50,255.50,255.50]
12.06 12:20:19 [Server] INFO [Minecraft-Server] [nutcase84: Teleported nutcase84 to 73.50,255.50,73.50]
12.06 12:19:37 [Server] INFO [Minecraft-Server] [nutcase84: Teleported nutcase84 to 0.50,255.50,0.50]
12.06 12:18:19 [Server] INFO [Minecraft-Server] [nutcase84: Teleported nutcase84 to 0.50,0.50,255.50]
12.06 12:17:35 [Server] INFO [Minecraft-Server] [nutcase84: Teleported nutcase84 to 64.50,64.50,255.50]
12.06 12:17:35 [Multicraft] Skipped 5 lines due to rate limit (30/s)
12.06 12:17:33 [Minecraft-Server] cool_girl76 ran command Message of the Day
12.06 12:17:33 [Server] INFO at net.minecraft.server.dedicated.DedicatedServerListenThread.func_71747_b(SourceFile:29)
12.06 12:17:33 [Server] INFO at net.minecraft.server.ServerListenThread.func_71766_a(ServerListenThread.java:55)
12.06 12:17:33 [Server] INFO at net.minecraft.network.NetLoginHandler.func_72532_c(NetLoginHandler.java:71)
12.06 12:17:33 [Server] INFO at net.minecraft.network.NetLoginHandler.func_72529_d(NetLoginHandler.java:178)
12.06 12:17:33 [Server] INFO at cpw.mods.fml.common.network.FMLNetworkHandler.onConnectionReceivedFromClient(FMLNetworkHandler.java:120)
12.06 12:17:33 [Server] INFO at cpw.mods.fml.common.network.FMLNetworkHandler.handleClientConnection(FMLNetworkHandler.java:166)
12.06 12:17:33 [Server] INFO at net.minecraft.network.NetLoginHandler.completeConnection(NetLoginHandler.java:194)
12.06 12:17:33 [Server] INFO at net.minecraft.server.management.ServerConfigurationManager.func_72355_a(ServerConfigurationManager.java:120)
12.06 12:17:33 [Server] INFO java.lang.NullPointerException
12.06 12:17:33 [Server] WARNING [Minecraft-Server] Failed to handle packet for cool_girl76 [/69.41.11.66:51324]: java.lang.NullPointerException
12.06 12:17:33 [Server] INFO at net.minecraft.server.ThreadMinecraftServer.run(SourceFile:573)
12.06 12:17:33 [Server] INFO at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:470)
12.06 12:17:33 [Server] INFO at net.minecraft.server.MinecraftServer.func_71217_p(MinecraftServer.java:572)
12.06 12:17:33 [Server] INFO at net.minecraft.server.dedicated.DedicatedServer.func_71190_q(DedicatedServer.java:275)
12.06 12:17:33 [Server] INFO at net.minecraft.server.MinecraftServer.func_71190_q(MinecraftServer.java:676)
12.06 12:17:33 [Server] INFO at net.minecraft.server.dedicated.DedicatedServerListenThread.func_71747_b(SourceFile:29)
12.06 12:17:33 [Server] INFO at net.minecraft.server.ServerListenThread.func_71766_a(ServerListenThread.java:55)
12.06 12:17:33 [Server] INFO at net.minecraft.network.NetLoginHandler.func_72532_c(NetLoginHandler.java:71)
12.06 12:17:33 [Server] INFO at net.minecraft.network.NetLoginHandler.func_72529_d(NetLoginHandler.java:178)
12.06 12:17:33 [Server] INFO at cpw.mods.fml.common.network.FMLNetworkHandler.onConnectionReceivedFromClient(FMLNetworkHandler.java:120)
12.06 12:17:33 [Server] INFO at cpw.mods.fml.common.network.FMLNetworkHandler.handleClientConnection(FMLNetworkHandler.java:166)
12.06 12:17:33 [Server] INFO at net.minecraft.network.NetLoginHandler.completeConnection(NetLoginHandler.java:194)
12.06 12:17:33 [Server] INFO at net.minecraft.server.management.ServerConfigurationManager.func_72355_a(ServerConfigurationManager.java:120)
12.06 12:17:33 [Server] INFO java.lang.NullPointerException
12.06 12:17:33 [Server] SEVERE Error handling login related packet - connection from cool_girl76 [/69.41.11.66:51324] refused
12.06 12:17:33 [Server] INFO [Minecraft-Server] Disconnecting cool_girl76 [/69.41.11.66:51324]: Internal server error
12.06 12:17:33 [Server] INFO Cannot Hotload Dim: Could not get provider type for dimension 13, does not exist
12.06 12:17:33 [Connect] User [Minecraft-Server] cool_girl76, IP 69.41.11.66
12.06 12:17:33 [Server] INFO Cannot Hotload Dim: Could not get provider type for dimension 13, does not exist
12.06 12:17:33 [Server] INFO User cool_girl76 connecting with mods [ComputerCraft, CCTurtle, BuildCraft|Core, BuildCraft|Factory, Forge, BuildCraft|Energy, BuildCraft|Silicon, BuildCraft|Builders, BuildCraft|Transport]
12.06 12:17:33 [Multicraft] Skipped 5 lines due to rate limit (30/s)
12.06 12:17:27 [Minecraft-Server] cool_girl76 ran command Message of the Day
12.06 12:17:26 [Server] INFO at net.minecraft.server.dedicated.DedicatedServerListenThread.func_71747_b(SourceFile:29)
12.06 12:17:26 [Server] INFO at net.minecraft.server.ServerListenThread.func_71766_a(ServerListenThread.java:55)
12.06 12:17:26 [Server] INFO at net.minecraft.network.NetLoginHandler.func_72532_c(NetLoginHandler.java:71)
12.06 12:17:26 [Server] INFO at net.minecraft.network.NetLoginHandler.func_72529_d(NetLoginHandler.java:178)
12.06 12:17:26 [Server] INFO at cpw.mods.fml.common.network.FMLNetworkHandler.onConnectionReceivedFromClient(FMLNetworkHandler.java:120)
12.06 12:17:26 [Server] INFO at cpw.mods.fml.common.network.FMLNetworkHandler.handleClientConnection(FMLNetworkHandler.java:166)
12.06 12:17:26 [Server] INFO at net.minecraft.network.NetLoginHandler.completeConnection(NetLoginHandler.java:194)
12.06 12:17:26 [Server] INFO at net.minecraft.server.management.ServerConfigurationManager.func_72355_a(ServerConfigurationManager.java:120)
12.06 12:17:26 [Server] INFO java.lang.NullPointerException
12.06 12:17:26 [Server] WARNING [Minecraft-Server] Failed to handle packet for cool_girl76 [/69.41.11.66:51318]: java.lang.NullPointerException
12.06 12:17:26 [Server] INFO at net.minecraft.server.ThreadMinecraftServer.run(SourceFile:573)
12.06 12:17:26 [Server] INFO at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:470)
12.06 12:17:26 [Server] INFO at net.minecraft.server.MinecraftServer.func_71217_p(MinecraftServer.java:572)
12.06 12:17:26 [Server] INFO at net.minecraft.server.dedicated.DedicatedServer.func_71190_q(DedicatedServer.java:275)
12.06 12:17:26 [Server] INFO at net.minecraft.server.MinecraftServer.func_71190_q(MinecraftServer.java:676)
12.06 12:17:26 [Server] INFO at net.minecraft.server.dedicated.DedicatedServerListenThread.func_71747_b(SourceFile:29)
12.06 12:17:26 [Server] INFO at net.minecraft.server.ServerListenThread.func_71766_a(ServerListenThread.java:55)
12.06 12:17:26 [Server] INFO at net.minecraft.network.NetLoginHandler.func_72532_c(NetLoginHandler.java:71)
12.06 12:17:26 [Server] INFO at net.minecraft.network.NetLoginHandler.func_72529_d(NetLoginHandler.java:178)
12.06 12:17:26 [Server] INFO at cpw.mods.fml.common.network.FMLNetworkHandler.onConnectionReceivedFromClient(FMLNetworkHandler.java:120)
12.06 12:17:26 [Server] INFO at cpw.mods.fml.common.network.FMLNetworkHandler.handleClientConnection(FMLNetworkHandler.java:166)
12.06 12:17:26 [Server] INFO at net.minecraft.network.NetLoginHandler.completeConnection(NetLoginHandler.java:194)
12.06 12:17:26 [Server] INFO at net.minecraft.server.management.ServerConfigurationManager.func_72355_a(ServerConfigurationManager.java:120)
12.06 12:17:26 [Server] INFO java.lang.NullPointerException
12.06 12:17:26 [Server] SEVERE Error handling login related packet - connection from cool_girl76 [/69.41.11.66:51318] refused
12.06 12:17:26 [Server] INFO [Minecraft-Server] Disconnecting cool_girl76 [/69.41.11.66:51318]: Internal server error
12.06 12:17:26 [Server] INFO Cannot Hotload Dim: Could not get provider type for dimension 13, does not exist
12.06 12:17:26 [Connect] User [Minecraft-Server] cool_girl76, IP 69.41.11.66
12.06 12:17:26 [Server] INFO Cannot Hotload Dim: Could not get provider type for dimension 13, does not exist
12.06 12:17:26 [Server] INFO User cool_girl76 connecting with mods [ComputerCraft, CCTurtle, BuildCraft|Core, BuildCraft|Factory, Forge, BuildCraft|Energy, BuildCraft|Silicon, BuildCraft|Builders, BuildCraft|Transport]
12.06 12:15:20 [Server] INFO [Minecraft-Server] [nutcase84: Teleported nutcase84 to 72.50,72.50,255.50]
12.06 12:15:13 [Server] INFO [Minecraft-Server] [nutcase84: Teleported nutcase84 to 72.50,72.50,255.50]
12.06 12:14:59 [Server] INFO [Minecraft-Server] [nutcase84: Teleported nutcase84 to 64.50,64.50,255.50]
12.06 12:14:51 [Server] INFO [Minecraft-Server] Saved the world
12.06 12:14:51 [Server] INFO [Minecraft-Server] Saving…
12.06 12:14:51 [Server] INFO [Minecraft-Server] Turned on world auto-saving
12.06 12:14:51 [Multicraft] Auto-saving world…
12.06 12:14:44 [Disconnect] User [Minecraft-Server] sling972 has disconnected, reason: disconnect.quitting
12.06 12:05:41 [Minecraft-Server] sling972 ran command Message of the Day
12.06 12:05:41 [Connect] User [Minecraft-Server] sling972, IP 173.225.198.112
12.06 12:05:41 [Server] INFO User sling972 connecting with mods [ComputerCraft, CCTurtle, BuildCraft|Core, BuildCraft|Factory, Forge, BuildCraft|Energy, BuildCraft|Silicon, BuildCraft|Builders, BuildCraft|Transport]
12.06 12:05:37 [Multicraft] Skipped 2 lines due to rate limit (30/s)
12.06 12:05:36 [Server] INFO at net.minecraft.server.MinecraftServer.func_71217_p(MinecraftServer.java:572)
12.06 12:05:36 [Server] INFO at net.minecraft.server.dedicated.DedicatedServer.func_71190_q(DedicatedServer.java:275)
12.06 12:05:36 [Server] INFO at net.minecraft.server.MinecraftServer.func_71190_q(MinecraftServer.java:676)
12.06 12:05:36 [Server] INFO at net.minecraft.server.dedicated.DedicatedServerListenThread.func_71747_b(SourceFile:30)
12.06 12:05:36 [Server] INFO at net.minecraft.network.NetworkListenThread.func_71747_b(NetworkListenThread.java:53)
12.06 12:05:36 [Server] INFO at net.minecraft.network.NetServerHandler.func_72570_d(NetServerHandler.java:134)
12.06 12:05:36 [Server] INFO at net.minecraft.network.TcpConnection.func_74428_b(TcpConnection.java:461)
12.06 12:05:36 [Server] INFO at net.minecraft.network.packet.Packet102WindowClick.func_73279_a(SourceFile:31)
12.06 12:05:36 [Server] INFO at net.minecraft.network.NetServerHandler.func_72523_a(NetServerHandler.java:897)
12.06 12:05:36 [Server] INFO at net.minecraft.inventory.Container.func_75144_a(SourceFile:190)
12.06 12:05:36 [Server] INFO at java.util.ArrayList.get(Unknown Source)
12.06 12:05:36 [Server] INFO at java.util.ArrayList.rangeCheck(Unknown Source)
12.06 12:05:36 [Server] INFO java.lang.IndexOutOfBoundsException: Index: 49, Size: 45
12.06 12:05:36 [Server] WARNING [Minecraft-Server] Failed to handle packet for sling972/173.225.198.112: java.lang.IndexOutOfBoundsException: Index: 49, Size: 45
12.06 12:05:36 [Server] INFO at net.minecraft.server.ThreadMinecraftServer.run(SourceFile:573)
12.06 12:05:36 [Server] INFO at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:470)
12.06 12:05:36 [Server] INFO at net.minecraft.server.MinecraftServer.func_71217_p(MinecraftServer.java:572)
12.06 12:05:36 [Server] INFO at net.minecraft.server.dedicated.DedicatedServer.func_71190_q(DedicatedServer.java:275)
12.06 12:05:36 [Server] INFO at net.minecraft.server.MinecraftServer.func_71190_q(MinecraftServer.java:676)
12.06 12:05:36 [Server] INFO at net.minecraft.server.dedicated.DedicatedServerListenThread.func_71747_b(SourceFile:30)
12.06 12:05:36 [Server] INFO at net.minecraft.network.NetworkListenThread.func_71747_b(NetworkListenThread.java:53)
12.06 12:05:36 [Server] INFO at net.minecraft.network.NetServerHandler.func_72570_d(NetServerHandler.java:134)
12.06 12:05:36 [Server] INFO at net.minecraft.network.TcpConnection.func_74428_b(TcpConnection.java:461)
12.06 12:05:36 [Server] INFO at net.minecraft.network.packet.Packet102WindowClick.func_73279_a(SourceFile:31)
12.06 12:05:36 [Server] INFO at net.minecraft.network.NetServerHandler.func_72523_a(NetServerHandler.java:897)
12.06 12:05:36 [Server] INFO at net.minecraft.inventory.Container.func_75144_a(SourceFile:190)
12.06 12:05:36 [Server] INFO at java.util.ArrayList.get(Unknown Source)
12.06 12:05:36 [Server] INFO at java.util.ArrayList.rangeCheck(Unknown Source)
12.06 12:05:36 [Server] INFO java.lang.IndexOutOfBoundsException: Index: 49, Size: 45
12.06 12:05:36 [Server] SEVERE A critical server error occured handling a packet, kicking 162613
12.06 12:04:50 [Server] INFO [Minecraft-Server] Saved the world
12.06 12:04:50 [Server] INFO [Minecraft-Server] Saving…
(The person's IGN is cool_girl76)