How to define a variable with simulated result

Hi, everyone, I am trying to run COMSOL file in COMSOL 4.4. My file originally works in COMSOL 3.5, but when i run it in COMSOL 4.4, one variable appears to be orange and I cannot get any result. I am trying to simulate a ultraviolet light go through a resin and cure the resin. my defined variable is related to the resin depth which is z axis value in the final result. I used to put z to define the relationship in COMSOL 3.5 and it works. I am wandering how I should define in COMSOL 4.4. I attached some photos to better illustrate the situation.
Thanks in advance.
Ying