In case there is still someone wondering about this, I have experienced LC freezing while trying to render a scene using caustics. I would recommend to turn on caustics just if you are completely certain about its settings. An error in the caustics settings can blow up your LC.
I have also experienced freezing of the LC when the network supporting a DR is not properly set up. Specifically, slaves not having access to resources in the model. I solved it by getting a network with a server that contains all textures or proxies.
So, appart from what said before me, also check caustics and DR settings.