when i log in the screen turn black and then this is showing

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--- BEGIN ERROR REPORT a1dce528 --------
Generated 22-09-10 10:47

Minecraft: Minecraft Alpha v1.1.2
OS: Windows 7 (amd64) version 6.1
Java: 1.6.0_21, Sun Microsystems Inc.
VM: Java HotSpot(TM) 64-Bit Server VM (mixed mode), Sun Microsystems Inc.
LWJGL: 2.3
OpenGL: GeForce GTX 260/PCI/SSE2 version 3.2.0, NVIDIA Corporation

java.lang.IllegalArgumentException: input == null!
at javax.imageio.ImageIO.read(Unknown Source)
at kd.<init>(SourceFile:27)
at net.minecraft.client.Minecraft.a(SourceFile:212)
at net.minecraft.client.Minecraft.run(SourceFile:554)
at java.lang.Thread.run(Unknown Source)
--- END ERROR REPORT 5c062f71 ----------