Creo 7.0.1.0 formula driven lattice freeze

I am trying to design  on creo 7 and my computer freezes whenever i select the custom lattice option. 

Anyone knows what the issue is.

My  computer specs: Hp dv6 Intel(R) Core(TM) i5-2430M CPU @ 2.40GHz 2.40 GHz

Ram: 8Gb