Feed the Beast Mod-pack Cannot connect to servers or create new worlds [closed]

When I log into FTB, using any of the new mod-packs, e.g. FTB Monster or Agrarian Skies, the game works fine until I try to create new world or log into a server.

If I try to create a new world FTB stops responding, I have left it alone for up to an hour afterwards for no effect. When I try to connect to a server I can see the server list, but if i try to connect it remains at 'Logging On'.

I have uploaded the console log and the error report to PasteBin.

The error message in the console is

2014-06-13 21:08:52 [SEVERE] [Minecraft-Server] Encountered an unexpected exception NoClassDefFoundError 
java.lang.NoClassDefFoundError: org/bouncycastle/jce/provider/BouncyCastleProvider 
at net.minecraft.server.integrated.IntegratedServer.func_71197_b(IntegratedServer.java:105) 
at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:445) 
at net.minecraft.server.ThreadMinecraftServer.run(SourceFile:583) 
Caused by: java.lang.ClassNotFoundException: org.bouncycastle.jce.provider.BouncyCastleProvider 
at java.net.URLClassLoader$1.run(Unknown Source) 
at java.net.URLClassLoader$1.run(Unknown Source) 
at java.security.AccessController.doPrivileged(Native Method) 
at java.net.URLClassLoader.findClass(Unknown Source) 
at net.minecraft.launchwrapper.LaunchClassLoader.findClass(LaunchClassLoader.java:113) 
at java.lang.ClassLoader.loadClass(Unknown Source) 
at java.lang.ClassLoader.loadClass(Unknown Source) 
... 3 more 

I have updated java and re-installed FTB several times.