When attempting to run my mod, the single player will run fine however when attempting to connect to a custom server the client crashes and, I get the following crash report.

 

Minecraft Crash Report ----

// Daisy, daisy...

 

Time: 12/19/13 1:10 AM

Description: Ticking screen

 

java.lang.NullPointerException

at java.net.URLEncoder.encode(Unknown Source)

at net.minecraft.client.multiplayer.NetClientHandler.urlEncode(NetClientHandler.java:336)

at net.minecraft.client.multiplayer.NetClientHandler.sendSessionRequest(NetClientHandler.java:318)

at net.minecraft.client.multiplayer.NetClientHandler.handleServerAuthData(NetClientHandler.java:299)

at net.minecraft.network.packet.Packet253ServerAuthData.processPacket(Packet253ServerAuthData.java:51)

at net.minecraft.network.TcpConnection.processReadPackets(TcpConnection.java:462)

at net.minecraft.client.multiplayer.NetClientHandler.processReadPackets(NetClientHandler.java:281)

at net.minecraft.client.multiplayer.GuiConnecting.updateScreen(GuiConnecting.java:51)

at net.minecraft.client.Minecraft.runTick(Minecraft.java:1580)

at net.minecraft.client.Minecraft.runGameLoop(Minecraft.java:910)

at net.minecraft.client.Minecraft.run(Minecraft.java:838)

at net.minecraft.client.main.Main.main(Main.java:93)

at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)

at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)

at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)

at java.lang.reflect.Method.invoke(Unknown Source)

at net.minecraft.launchwrapper.Launch.launch(Launch.java:131)

at net.minecraft.launchwrapper.Launch.main(Launch.java:27)

 

 

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

---------------------------------------------------------------------------------------

 

-- Head --

Stacktrace:

at java.net.URLEncoder.encode(Unknown Source)

at net.minecraft.client.multiplayer.NetClientHandler.urlEncode(NetClientHandler.java:336)

at net.minecraft.client.multiplayer.NetClientHandler.sendSessionRequest(NetClientHandler.java:318)

at net.minecraft.client.multiplayer.NetClientHandler.handleServerAuthData(NetClientHandler.java:299)

at net.minecraft.network.packet.Packet253ServerAuthData.processPacket(Packet253ServerAuthData.java:51)

at net.minecraft.network.TcpConnection.processReadPackets(TcpConnection.java:462)

at net.minecraft.client.multiplayer.NetClientHandler.processReadPackets(NetClientHandler.java:281)

at net.minecraft.client.multiplayer.GuiConnecting.updateScreen(GuiConnecting.java:51)

 

-- Affected screen --

Details:

Screen name: net.minecraft.client.multiplayer.GuiConnecting

Stacktrace:

at net.minecraft.client.Minecraft.runTick(Minecraft.java:1580)

at net.minecraft.client.Minecraft.runGameLoop(Minecraft.java:910)

at net.minecraft.client.Minecraft.run(Minecraft.java:838)

at net.minecraft.client.main.Main.main(Main.java:93)

at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)

at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)

at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)

at java.lang.reflect.Method.invoke(Unknown Source)

at net.minecraft.launchwrapper.Launch.launch(Launch.java:131)

at net.minecraft.launchwrapper.Launch.main(Launch.java:27)

 

-- System Details --

Details:

Minecraft Version: 1.6.4

Operating System: Windows 8 (x86) version 6.2

Java Version: 1.7.0_45, Oracle Corporation

Java VM Version: Java HotSpot Client VM (mixed mode), Oracle Corporation

Memory: 985251688 bytes (939 MB) / 1046937600 bytes (998 MB) up to 1046937600 bytes (998 MB)

JVM Flags: 3 total; -Xincgc -Xmx1024M -Xms1024M

AABB Pool Size: 0 (0 bytes; 0 MB) allocated, 0 (0 bytes; 0 MB) used

Suspicious classes: FML and Forge are installed

IntCache: cache: 0, tcache: 0, allocated: 0, tallocated: 0

FML: MCP v8.11 FML v6.4.45.953 Minecraft Forge 9.11.1.953 4 mods loaded, 4 mods active

mcp{8.09} [Minecraft Coder Pack] (minecraft.jar) Unloaded->Constructed->Pre-initialized->Initialized->Post-initialized->Available

FML{6.4.45.953} [Forge Mod Loader] (bin) Unloaded->Constructed->Pre-initialized->Initialized->Post-initialized->Available

Forge{9.11.1.953} [Minecraft Forge] (bin) Unloaded->Constructed->Pre-initialized->Initialized->Post-initialized->Available

GizLabs{v1} [GizLabs Core] (bin) Unloaded->Constructed->Pre-initialized->Initialized->Post-initialized->Available

Launched Version: 1.6

LWJGL: 2.9.0

OpenGL: Intel® HD Graphics 4000 GL version 4.0.0 - Build 9.17.10.2867, Intel

Is Modded: Definitely; Client brand changed to 'fml,forge'

Type: Client (map_client.txt)

Resource Pack: Default

Current Language: English (US)

Profiler Position: N/A (disabled)

Vec3 Pool Size: ~~ERROR~~ NullPointerException: null

 

any idea what this would occur?

I had a similar issue lately, but I am foggy to remember the exact details... but if you client is running from the IDE, the server needs to be in offline mode. Just grasping at straws (Btw, server run from IDE is not in offline mode)

Actually I just resolved the problem, I was having an ID Conflict, with a vanilla item, also the server for me at least does start in offline mode however in your error log look for ID conflicts mine was with a record.