Trying to make a "hopper Pipe" Had Diamond Blocks running through. On of th hoppers turned into a furnace and when I clicked it it crashed the game and gave me this Screen. (full file report is included.)

Minecraft has crashed!
----------------------

Minecraft has stopped running because it encountered a problem; Ticking memory connection

A full error report has been saved to C:\Users\Dominic\AppData\Roaming\.minecraft\crash-reports\crash-2013-01-06_17.57.23-server.txt - Please include a copy of that file (Not this screen!) if you report this crash to anyone; without it, they will not be able to help fix the crash

— BEGIN ERROR REPORT 455a9ed7 --------
Full report at:
C:\Users\Dominic\AppData\Roaming\.minecraft\crash-reports\crash-2013-01-06_17.57.23-server.txtMin
Please show that file to Mojang, NOT just this screen!

Generated 1/6/13 5:57 PM

– System Details –
Details:
Minecraft Version: 13w01b
Operating System: Windows 7 (x86) version 6.1
Java Version: 1.7.0_10, Oracle Corporation
Java VM Version: Java HotSpot(TM) Client VM (mixed mode), Oracle Corporation
Memory: 265569624 bytes (253 MB) / 519110656 bytes (495 MB) up to 1037959168 bytes (989 MB)
JVM Flags: 2 total; -Xms512m -Xmx1024m
AABB Pool Size: 982 (54992 bytes; 0 MB) allocated, 825 (46200 bytes; 0 MB) used
Suspicious classes: No suspicious classes found.
IntCache: cache: 0, tcache: 0, allocated: 0, tallocated: 0
Profiler Position: N/A (disabled)
Vec3 Pool Size: 288 (16128 bytes; 0 MB) allocated, 263 (14728 bytes; 0 MB) used
Player Count: 1 / 8; [iq['dtschaedler'/23, l='New World', x=-739.65, y=4.00, z=-752.57]]
Type: Integrated Server (map_client.txt)
Is Modded: Probably not. Jar signature remains and both client + server brands are untouched.

java.lang.ClassCastException: aob cannot be cast to aoa
at akl.a(SourceFile:111)
at ir.a(SourceFile:240)
at iv.a(SourceFile:367)
at fk.a(SourceFile:58)
at cf.b(SourceFile:55)
at iv.d(SourceFile:57)
at iw.b(SourceFile:39)
at beq.b(SourceFile:84)
at net.minecraft.server.MinecraftServer.r(SourceFile:762)
at net.minecraft.server.MinecraftServer.q(SourceFile:679)
at ben.q(SourceFile:117)
at net.minecraft.server.MinecraftServer.run(SourceFile:613)
at fy.run(SourceFile:849)
— END ERROR REPORT b694dd61 ----------