Attempting to chat in game from specific computer causes crash

What I expected to happen was...:
The chat message should have transmitted to everyone on the server.

What actually happened was...:
Minecraft crashes

Steps to Reproduce:
1. Open Minecraft Launcher
2. Run Minecraft
3. Connect to any server
4. Press T and type a message.
5. Press Enter
Minecraft will then crash with the following error report:

---- Minecraft Crash Report ----
// Hi. I'm Minecraft, and I'm a crashaholic.

Time: 7/5/13 12:51 PM
Description: Deserializing Message

java.lang.ClassCastException: com.google.gson.JsonPrimitive cannot be cast to com.google.gson.JsonObject
at cw.a(SourceFile:14)
at cw.deserialize(SourceFile:10)
at com.google.gson.TreeTypeAdapter.read(TreeTypeAdapter.java:58)
at com.google.gson.Gson.fromJson(Gson.java:795)
at com.google.gson.Gson.fromJson(Gson.java:761)
at com.google.gson.Gson.fromJson(Gson.java:710)
at com.google.gson.Gson.fromJson(Gson.java:682)
at cu.c(SourceFile:220)
at bcn.a(SourceFile:518)
at dl.a(SourceFile:49)
at cn.b(SourceFile:350)
at bcn.d(SourceFile:95)
at bcu.b(SourceFile:60)
at atn.k(SourceFile:1380)
at atn.S(SourceFile:662)
at atn.d(SourceFile:618)
at net.minecraft.client.main.Main.main(SourceFile:101)

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

– Head –
Stacktrace:
at cw.a(SourceFile:14)
at cw.deserialize(SourceFile:10)
at com.google.gson.TreeTypeAdapter.read(TreeTypeAdapter.java:58)
at com.google.gson.Gson.fromJson(Gson.java:795)
at com.google.gson.Gson.fromJson(Gson.java:761)
at com.google.gson.Gson.fromJson(Gson.java:710)
at com.google.gson.Gson.fromJson(Gson.java:682)

– Serialized Message –
Details:
JSON string: Cannot send chat message.
Stacktrace:
at cu.c(SourceFile:220)
at bcn.a(SourceFile:518)
at dl.a(SourceFile:49)
at cn.b(SourceFile:350)
at bcn.d(SourceFile:95)

– Affected level –
Details:
Level name: MpServer
All players: 2 total; [bcx['SponAsylumGuest'/559938, l='MpServer', x=-4987.43, y=8.59, z=506.32], ben['SponQ'/532148, l='MpServer', x=-4987.13, y=5.41, z=513.50]]
Chunk stats: MultiplayerChunkCache: 275
Level seed: 0
Level generator: ID 01 - flat, ver 0. Features enabled: false
Level generator options:
Level spawn location: World: (-250,74,314), Chunk: (at 6,4,10 in -16,19; contains blocks -256,0,304 to -241,255,319), Region: (-1,0; contains chunks -32,0 to -1,31, blocks -512,0,0 to -1,255,511)
Level time: 435789962 game time, 440766044 day time
Level dimension: 0
Level storage version: 0x00000 - Unknown?
Level weather: Rain time: 0 (now: false), thunder time: 0 (now: false)
Level game mode: Game mode: creative (ID 1). Hardcore: false. Cheats: false
Forced entities: 47 total; [ob['entity.LeashKnot.name'/548192, l='MpServer', x=-4923.50, y=6.50, z=525.50], bcx['SponAsylumGuest'/559938, l='MpServer', x=-4987.43, y=8.59, z=506.32], rp['Horse'/546999, l='MpServer', x=-4925.50, y=4.00, z=523.50], rp['Horse'/559123, l='MpServer', x=-4945.81, y=4.00, z=471.94], rp['Horse'/547776, l='MpServer', x=-4920.50, y=4.00, z=523.50], rp['Horse'/550575, l='MpServer', x=-4923.66, y=4.00, z=516.88], rp['Horse'/555258, l='MpServer', x=-4910.28, y=2.00, z=522.19], ob['entity.LeashKnot.name'/547110, l='MpServer', x=-4925.50, y=6.50, z=525.50], rp['Horse'/548081, l='MpServer', x=-4922.50, y=4.00, z=523.50], rp['Horse'/555259, l='MpServer', x=-4945.64, y=5.00, z=528.76], ben['SponQ'/532148, l='MpServer', x=-4987.13, y=5.41, z=513.50], rp['Horse'/550344, l='MpServer', x=-4916.50, y=4.00, z=517.50], ob['entity.LeashKnot.name'/551921, l='MpServer', x=-4919.50, y=6.50, z=515.50], rp['Horse'/551920, l='MpServer', x=-4920.66, y=4.00, z=517.66], rp['Horse'/547465, l='MpServer', x=-4916.66, y=4.00, z=524.28], ob['entity.LeashKnot.name'/550579, l='MpServer', x=-4922.50, y=6.50, z=515.50], rp['Horse'/554885, l='MpServer', x=-4909.16, y=2.00, z=527.94], ob['entity.LeashKnot.name'/546695, l='MpServer', x=-4928.50, y=6.50, z=525.50], ob['entity.LeashKnot.name'/539408, l='MpServer', x=-4945.50, y=5.50, z=522.50], rp['Horse'/550100, l='MpServer', x=-4928.34, y=4.00, z=516.91], ob['entity.LeashKnot.name'/557266, l='MpServer', x=-4932.50, y=6.50, z=542.50], rp['Horse'/559087, l='MpServer', x=-4991.30, y=5.02, z=504.98], rp['Horse'/554886, l='MpServer', x=-4958.88, y=6.00, z=510.95], rp['Horse'/555336, l='MpServer', x=-4909.74, y=2.00, z=531.11], rw['Sheep'/537313, l='MpServer', x=-5027.91, y=4.00, z=531.13], rw['Sheep'/537312, l='MpServer', x=-5053.66, y=4.00, z=517.19], rw['Sheep'/537314, l='MpServer', x=-5047.72, y=4.00, z=455.38], rp['Horse'/546405, l='MpServer', x=-4928.34, y=4.00, z=524.28], ob['entity.LeashKnot.name'/539319, l='MpServer', x=-4948.50, y=5.50, z=522.50], ob['entity.LeashKnot.name'/557225, l='MpServer', x=-4925.50, y=6.50, z=515.50], rv['Pig'/537316, l='MpServer', x=-4957.19, y=4.00, z=569.09], rp['Horse'/559066, l='MpServer', x=-4946.16, y=4.00, z=470.22], ben['SponQ'/532148, l='MpServer', x=-4987.13, y=5.41, z=513.50], ob['entity.LeashKnot.name'/550474, l='MpServer', x=-4916.50, y=6.50, z=515.50], rp['Horse'/554873, l='MpServer', x=-4907.94, y=2.00, z=523.20], rp['Horse'/537327, l='MpServer', x=-4944.59, y=5.00, z=520.91], rp['Horse'/550242, l='MpServer', x=-4925.34, y=4.00, z=516.72], ob['entity.LeashKnot.name'/547905, l='MpServer', x=-4920.50, y=6.50, z=525.50], rp['Horse'/537330, l='MpServer', x=-4946.28, y=4.73, z=519.84], rw['Sheep'/537332, l='MpServer', x=-4952.19, y=4.00, z=450.69], ob['entity.LeashKnot.name'/550141, l='MpServer', x=-4928.50, y=6.50, z=515.50], rw['Sheep'/537333, l='MpServer', x=-4969.91, y=4.00, z=449.91], rp['Horse'/559142, l='MpServer', x=-4960.88, y=4.00, z=470.50], ob['entity.LeashKnot.name'/547633, l='MpServer', x=-4916.50, y=6.50, z=525.50], rp['Horse'/559145, l='MpServer', x=-4948.63, y=4.00, z=448.19], rp['Horse'/555753, l='MpServer', x=-4931.81, y=4.00, z=541.72], rp['Horse'/555752, l='MpServer', x=-4957.05, y=6.00, z=510.56]]
Retry entities: 0 total; []
Stacktrace:
at bcu.a(SourceFile:284)
at atn.k(SourceFile:1387)
at atn.S(SourceFile:662)
at atn.d(SourceFile:618)
at net.minecraft.client.main.Main.main(SourceFile:101)

– Affected level –
Details:
Level name: MpServer
All players: 2 total; [bcx['SponAsylumGuest'/559938, l='MpServer', x=-4987.43, y=8.59, z=506.32], ben['SponQ'/532148, l='MpServer', x=-4987.13, y=5.41, z=513.50]]
Chunk stats: MultiplayerChunkCache: 275
Level seed: 0
Level generator: ID 01 - flat, ver 0. Features enabled: false
Level generator options:
Level spawn location: World: (-250,74,314), Chunk: (at 6,4,10 in -16,19; contains blocks -256,0,304 to -241,255,319), Region: (-1,0; contains chunks -32,0 to -1,31, blocks -512,0,0 to -1,255,511)
Level time: 435789962 game time, 440766044 day time
Level dimension: 0
Level storage version: 0x00000 - Unknown?
Level weather: Rain time: 0 (now: false), thunder time: 0 (now: false)
Level game mode: Game mode: creative (ID 1). Hardcore: false. Cheats: false
Forced entities: 47 total; [ob['entity.LeashKnot.name'/548192, l='MpServer', x=-4923.50, y=6.50, z=525.50], bcx['SponAsylumGuest'/559938, l='MpServer', x=-4987.43, y=8.59, z=506.32], rp['Horse'/546999, l='MpServer', x=-4925.50, y=4.00, z=523.50], rp['Horse'/559123, l='MpServer', x=-4945.81, y=4.00, z=471.94], rp['Horse'/547776, l='MpServer', x=-4920.50, y=4.00, z=523.50], rp['Horse'/550575, l='MpServer', x=-4923.66, y=4.00, z=516.88], rp['Horse'/555258, l='MpServer', x=-4910.28, y=2.00, z=522.19], ob['entity.LeashKnot.name'/547110, l='MpServer', x=-4925.50, y=6.50, z=525.50], rp['Horse'/548081, l='MpServer', x=-4922.50, y=4.00, z=523.50], rp['Horse'/555259, l='MpServer', x=-4945.64, y=5.00, z=528.76], ben['SponQ'/532148, l='MpServer', x=-4987.13, y=5.41, z=513.50], rp['Horse'/550344, l='MpServer', x=-4916.50, y=4.00, z=517.50], ob['entity.LeashKnot.name'/551921, l='MpServer', x=-4919.50, y=6.50, z=515.50], rp['Horse'/551920, l='MpServer', x=-4920.66, y=4.00, z=517.66], rp['Horse'/547465, l='MpServer', x=-4916.66, y=4.00, z=524.28], ob['entity.LeashKnot.name'/550579, l='MpServer', x=-4922.50, y=6.50, z=515.50], rp['Horse'/554885, l='MpServer', x=-4909.16, y=2.00, z=527.94], ob['entity.LeashKnot.name'/546695, l='MpServer', x=-4928.50, y=6.50, z=525.50], ob['entity.LeashKnot.name'/539408, l='MpServer', x=-4945.50, y=5.50, z=522.50], rp['Horse'/550100, l='MpServer', x=-4928.34, y=4.00, z=516.91], ob['entity.LeashKnot.name'/557266, l='MpServer', x=-4932.50, y=6.50, z=542.50], rp['Horse'/559087, l='MpServer', x=-4991.30, y=5.02, z=504.98], rp['Horse'/554886, l='MpServer', x=-4958.88, y=6.00, z=510.95], rp['Horse'/555336, l='MpServer', x=-4909.74, y=2.00, z=531.11], rw['Sheep'/537313, l='MpServer', x=-5027.91, y=4.00, z=531.13], rw['Sheep'/537312, l='MpServer', x=-5053.66, y=4.00, z=517.19], rw['Sheep'/537314, l='MpServer', x=-5047.72, y=4.00, z=455.38], rp['Horse'/546405, l='MpServer', x=-4928.34, y=4.00, z=524.28], ob['entity.LeashKnot.name'/539319, l='MpServer', x=-4948.50, y=5.50, z=522.50], ob['entity.LeashKnot.name'/557225, l='MpServer', x=-4925.50, y=6.50, z=515.50], rv['Pig'/537316, l='MpServer', x=-4957.19, y=4.00, z=569.09], rp['Horse'/559066, l='MpServer', x=-4946.16, y=4.00, z=470.22], ben['SponQ'/532148, l='MpServer', x=-4987.13, y=5.41, z=513.50], ob['entity.LeashKnot.name'/550474, l='MpServer', x=-4916.50, y=6.50, z=515.50], rp['Horse'/554873, l='MpServer', x=-4907.94, y=2.00, z=523.20], rp['Horse'/537327, l='MpServer', x=-4944.59, y=5.00, z=520.91], rp['Horse'/550242, l='MpServer', x=-4925.34, y=4.00, z=516.72], ob['entity.LeashKnot.name'/547905, l='MpServer', x=-4920.50, y=6.50, z=525.50], rp['Horse'/537330, l='MpServer', x=-4946.28, y=4.73, z=519.84], rw['Sheep'/537332, l='MpServer', x=-4952.19, y=4.00, z=450.69], ob['entity.LeashKnot.name'/550141, l='MpServer', x=-4928.50, y=6.50, z=515.50], rw['Sheep'/537333, l='MpServer', x=-4969.91, y=4.00, z=449.91], rp['Horse'/559142, l='MpServer', x=-4960.88, y=4.00, z=470.50], ob['entity.LeashKnot.name'/547633, l='MpServer', x=-4916.50, y=6.50, z=525.50], rp['Horse'/559145, l='MpServer', x=-4948.63, y=4.00, z=448.19], rp['Horse'/555753, l='MpServer', x=-4931.81, y=4.00, z=541.72], rp['Horse'/555752, l='MpServer', x=-4957.05, y=6.00, z=510.56]]
Retry entities: 0 total; []

– System Details –
Details:
Minecraft Version: 1.6.1
Operating System: Windows XP (x86) version 5.1
Java Version: 1.6.0_17, Sun Microsystems Inc.
Java VM Version: Java HotSpot(TM) Client VM (mixed mode), Sun Microsystems Inc.
Memory: 9716672 bytes (9 MB) / 67108864 bytes (64 MB) up to 1065484288 bytes (1016 MB)
JVM Flags: 1 total; -Xmx1G
AABB Pool Size: 22216 (1244096 bytes; 1 MB) allocated, 690 (38640 bytes; 0 MB) used
Suspicious classes: No suspicious classes found.
IntCache: cache: 0, tcache: 0, allocated: 0, tallocated: 0
Launched Version: 1.6.1
LWJGL: 2.9.0
OpenGL: Quadro NVS 135M/PCI/SSE2 GL version 3.2.0, NVIDIA Corporation
Is Modded: Probably not. Jar signature remains and client brand is untouched.
Type: Client (map_client.txt)
Resource Pack: Default
Profiler Position: N/A (disabled)
Vec3 Pool Size: 617 (34552 bytes; 0 MB) allocated, 82 (4592 bytes; 0 MB) used