No se puede jugar al modo online me sale como un tipo de error me sale esto :

---- Minecraft Crash Report ----
// There are four lights!

Time: 31/03/14 19:04
Description: Rendering screen

java.lang.IllegalArgumentException: bad Base64 input character at 7166: 64 (decimal)
at io.netty.handler.codec.base64.Base64.decode(Base64.java:247)
at io.netty.handler.codec.base64.Base64.decode(Base64.java:197)
at io.netty.handler.codec.base64.Base64.decode(Base64.java:188)
at bhc.b(SourceFile:155)
at bhc.a(SourceFile:130)
at bbd.a(SourceFile:26)
at bbi.b(SourceFile:382)
at bbi.a(SourceFile:259)
at bgz.a(SourceFile:283)
at bms.b(SourceFile:852)
at azl.ah(SourceFile:784)
at azl.f(SourceFile:711)
at net.minecraft.client.main.Main.main(SourceFile:148)

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

– Head –
Stacktrace:
at io.netty.handler.codec.base64.Base64.decode(Base64.java:247)
at io.netty.handler.codec.base64.Base64.decode(Base64.java:197)
at io.netty.handler.codec.base64.Base64.decode(Base64.java:188)
at bhc.b(SourceFile:155)
at bhc.a(SourceFile:130)
at bbd.a(SourceFile:26)
at bbi.b(SourceFile:382)
at bbi.a(SourceFile:259)
at bgz.a(SourceFile:283)

– Screen render details –
Details:
Screen name: bgz
Mouse location: Scaled: (202, 145). Absolute: (404, 189)
Screen size: Scaled: (427, 240). Absolute: (854, 480). Scale factor of 2
Stacktrace:
at bms.b(SourceFile:852)
at azl.ah(SourceFile:784)
at azl.f(SourceFile:711)
at net.minecraft.client.main.Main.main(SourceFile:148)

– System Details –
Details:
Minecraft Version: 1.7.5
Operating System: Windows 8 (x86) version 6.2
Java Version: 1.7.0_51, Oracle Corporation
Java VM Version: Java HotSpot(TM) Client VM (mixed mode, sharing), Oracle Corporation
Memory: 34768800 bytes (33 MB) / 69931008 bytes (66 MB) up to 518979584 bytes (494 MB)
JVM Flags: 2 total; -XX:HeapDumpPath=MojangTricksIntelDriversForPerformance_javaw.exe_minecraft.exe.heapdump -Xmx512M
AABB Pool Size: 0 (0 bytes; 0 MB) allocated, 0 (0 bytes; 0 MB) used
IntCache: cache: 0, tcache: 0, allocated: 0, tallocated: 0
Launched Version: 1.7.5
LWJGL: 2.9.1
OpenGL: Intel(R) HD Graphics 4000 GL version 4.0.0 - Build 9.18.10.3224, Intel
GL Caps: Using GL 1.3 multitexturing.
Using framebuffer objects because OpenGL 3.0 is supported and separate blending is supported.
Anisotropic filtering is supported and maximum anisotropy is 16.
Shaders are available because OpenGL 2.1 is supported.

Is Modded: Probably not. Jar signature remains and client brand is untouched.
Type: Client (map_client.txt)
Resource Packs: []
Current Language: Español (México)
Profiler Position: N/A (disabled)
Vec3 Pool Size: 0 (0 bytes; 0 MB) allocated, 0 (0 bytes; 0 MB) used
Anisotropic Filtering: Off (1)