I dont Know why but I cant Play Minecaft::

Every Time, im Logging in , it Download packages (if they're avaiable) then It Shows The "Majong Specifications" But then it Says :

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

Minecraft has stopped running because it encountered a problem.

If you wish to report this, please copy this entire text and email it to support@mojang.com.
Please include a description of what you did when the error occured.

--- BEGIN ERROR REPORT a1dce528 --------
Generated 22.01.11 09:14

Minecraft: Minecraft Beta 1.2_02
OS: Windows 7 (x86) version 6.1
Java: 1.6.0_22, Sun Microsystems Inc.
VM: Java HotSpot(TM) Client VM (mixed mode), Sun Microsystems Inc.
LWJGL: 2.4.2
OpenGL: GeForce GT 320/PCI/SSE2 version 3.2.0, NVIDIA Corporation

java.nio.BufferOverflowException
 at java.nio.DirectByteBuffer.put(Unknown Source)
 at java.nio.ByteBuffer.put(Unknown Source)
 at gs.a(SourceFile:148)
 at gs.a(SourceFile:62)
 at net.minecraft.client.Minecraft.i(SourceFile:1086)
 at net.minecraft.client.Minecraft.run(SourceFile:642)
 at java.lang.Thread.run(Unknown Source)
--- END ERROR REPORT 4d5d30a4 ----------

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Can Anyone Help me please ?