Windows .jar Why is my Ftb stopping when starting up certain mod packs

[yoshi4211]

Ok, so ever since I have started to use ftb I've been encountering this problem where when I click launch on a modpack that is Horizons, RPG immersion, and Ultimate (and these are only the ones I know of) it kinda downloads it the first time then starts up but midway through starting up it just stops and says Error: Could not find or load main class net.minecraft.launchwrapper.Launch but it seams to only do this for Horizons with the other one it dosen't even say error
Added URL to classpath: file:/C:/Users/Myname/Downloads/divinerpg/instMods/liteloader.zip
Added URL to classpath: file:/C:/Users/Myname/Downloads/divinerpg/instMods/MinecraftForge.zip
Added URL to classpath: file:/C:/Users/Myname/Downloads/divinerpg/minecraft/bin/minecraft.jar
Added URL to classpath: file:/C:/Users/Myname/Downloads/divinerpg/minecraft/bin/lwjgl.jar
Added URL to classpath: file:/C:/Users/Myname/Downloads/divinerpg/minecraft/bin/lwjgl_util.jar
Added URL to classpath: file:/C:/Users/Myname/Downloads/divinerpg/minecraft/bin/jinput.jar
Loading natives...
Natives loaded...
Loading minecraft class
mc = class net.minecraft.client.Minecraft
and then it just stops.
Please help me what do I do how do I fix it

 

[lavarthan]

The only known possible fix is a force update. Look here for more info. On a helping note you should change the launcher folder to a folder on your desktop named FTB that is the recommended way use this guide to do it.