I logged onto Minecraft, went from the main log-in screen and when it the main screen should have loaded there was a pause and then an unexpected error message appeared.
What should have happened is that I, after logging into Minecraft, be able to select the type of game that I wanted to play.

After logging onto Minecraft, the game crashed.

Log on to Minecraft,wait for about ten seconds and then an Unexpected Error message appeared.

Because I cannot find the file here is the crash report.
A detailed walkthrough of the error, its code path and all known details is as follows:
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– System Details –
Details:
Minecraft Version: 1.5
Operating System: Mac OS X (x86_64) version 10.5.8
Java Version: 1.6.0_26, Apple Inc.
Java VM Version: Java HotSpot(TM) 64-Bit Server VM (mixed mode), Apple Inc.
Memory: 482836800 bytes (460 MB) / 534708224 bytes (509 MB) up to 1069416448 bytes (1019 MB)
JVM Flags: 3 total; -Xbootclasspath/a:/System/Library/PrivateFrameworks/JavaApplicationLauncher.framework/Resources/LauncherSupport.jar -Xms512M -Xmx1024M
AABB Pool Size: 0 (0 bytes; 0 MB) allocated, 0 (0 bytes; 0 MB) used
Suspicious classes: No suspicious classes found.
IntCache: cache: 0, tcache: 0, allocated: 0, tallocated: 0
LWJGL: 2.4.2
OpenGL: Intel GMA X3100 OpenGL Engine GL version 1.2 APPLE-1.5.48, Intel Inc.
Is Modded: Probably not. Jar signature remains and client brand is untouched.
Type: Client (map_client.txt)
Texture Pack: Default
Profiler Position: N/A (disabled)
Vec3 Pool Size: ~_ERROR~ NullPointerException: null