This is the crash report
---- Minecraft Crash Report ----
// Why did you do that?

Time: 8/18/14 5:09 PM
Description: Rendering screen

java.lang.IllegalArgumentException: bad Base64 input character at 13484: 191 (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 bgc.b(SourceFile:155)
at bgc.a(SourceFile:130)
at bch.a(SourceFile:26)
at bcm.b(SourceFile:382)
at bcm.a(SourceFile:259)
at bfz.a(SourceFile:283)
at blt.b(SourceFile:852)
at bao.ak(SourceFile:801)
at bao.f(SourceFile:728)
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 bgc.b(SourceFile:155)
at bgc.a(SourceFile:130)
at bch.a(SourceFile:26)
at bcm.b(SourceFile:382)
at bcm.a(SourceFile:259)
at bfz.a(SourceFile:283)

– Screen render details –
Details:
Screen name: bfz
Mouse location: Scaled: (369, 53). Absolute: (739, 373)
Screen size: Scaled: (427, 240). Absolute: (854, 480). Scale factor of 2
Stacktrace:
at blt.b(SourceFile:852)
at bao.ak(SourceFile:801)
at bao.f(SourceFile:728)
at net.minecraft.client.main.Main.main(SourceFile:148)

– System Details –
Details:
Minecraft Version: 1.7.10
Operating System: Mac OS X (x86_64) version 10.9.4
Java Version: 1.6.0_65, Apple Inc.
Java VM Version: Java HotSpot(TM) 64-Bit Server VM (mixed mode), Apple Inc.
Memory: 32240336 bytes (30 MB) / 170496000 bytes (162 MB) up to 1060372480 bytes (1011 MB)
JVM Flags: 5 total; -Xmx1G -XX:+UseConcMarkSweepGC -XX:+CMSIncrementalMode -XX:-UseAdaptiveSizePolicy -Xmn128M
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: 1.7.10
LWJGL: 2.9.1
OpenGL: Intel HD Graphics 4000 OpenGL Engine GL version 2.1 INTEL-8.28.30, Intel Inc.
GL Caps: Using GL 1.3 multitexturing.
Using framebuffer objects because ARB_framebuffer_object 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: English (UK)
Profiler Position: N/A (disabled)
Vec3 Pool Size: 0 (0 bytes; 0 MB) allocated, 0 (0 bytes; 0 MB) used
Anisotropic Filtering: Off (1)

So it crashes everytime i scroll down the multiplayer menu please help fix as soon as possible
Thanks