Instance folder is:
C:\Users\Renz\Documents\MultiMC\instances\Modded 1.5.1\minecraft\

Instance started with command:
"c:\program files\java\jre7\bin\java.exe" -XX:PermSize=128M -Xms1024m -Xmx2048m -jar MultiMCLauncher.jar  "Offline" "Offline" "MultiMC: Modded 1.5.1" "854x480" "Mojang"

Loading jars...
Loading URL: file:/C:/Users/Renz/Documents/MultiMC/instances/Modded%201.5.1/minecraft/bin/minecraft.jar
Loading URL: file:/C:/Users/Renz/Documents/MultiMC/instances/Modded%201.5.1/minecraft/bin/lwjgl.jar
Loading URL: file:/C:/Users/Renz/Documents/MultiMC/instances/Modded%201.5.1/minecraft/bin/lwjgl_util.jar
Loading URL: file:/C:/Users/Renz/Documents/MultiMC/instances/Modded%201.5.1/minecraft/bin/jinput.jar
Loading natives...
Exception in thread "main" java.lang.VerifyError: (class: net/minecraft/client/Minecraft, method: l signature: ()V) Incompatible argument to function
	at java.lang.Class.getDeclaredFields0(Native Method)
	at java.lang.Class.privateGetDeclaredFields(Unknown Source)
	at java.lang.Class.getDeclaredFields(Unknown Source)
	at MultiMCLauncher.getMCPathField(MultiMCLauncher.java:312)
	at MultiMCLauncher.main(MultiMCLauncher.java:159)
Minecraft exited with code 1.
Minecraft has crashed!