Why is the Network Link Conditioner preference pane crashing as soon as I turn it on?
Just a quick note to say that I eventually stopped the crashing by manually copying these two files from another OS X machine and then manually starting the nlcd daemon
(if you don't have another Mac, I posted my copies of those files here)

Copied these files:
/System/Library/LaunchDaemons/com.apple.NetworkLinkConditioner.plist
/usr/libexec/nlcd
Run these three commands:  

sudo chown root /System/Library/LaunchDaemons/com.apple.NetworkLinkConditioner.plist      
sudo chmod 644 /System/Library/LaunchDaemons/com.apple.NetworkLinkConditioner.plist   
sudo launchctl load /System/Library/LaunchDaemons/com.apple.NetworkLinkConditioner.plist


After that the pref pane didn't unexpectedly exit when moving the switch to 'on'.

Taken from https://devforums.apple.com/message/645980#645980