Optimisation problem in CATIA V5

Hello. I am working with CATIA V5 software, recently faced with a problem which I can't figure out by myself and would really appreciate if somebody could help me with it. The problem is that I am designing an engine pylon for my final project at Uni. I created two models which I want to optimise. The first one was made hastily, without any parameters, the second one was made using specific parameters in the gen design. For the first model the simulation is running well, the only problem is that I need to search for every single line I want to be changed which is extremely hard because as you understand there are dozens of them. For the second model it is much easier to select all the lines I want to be changed since they are connected with a definite parameter, but here is where the problem occurs, before optimisation everything goes as it should, but during the optimisation all parameters values are missing and they are changing to 0 automatically and as a result, CATIA can't give me any optimised model. I tried to fix it by locking parameters values, but if I am doing this it is impossible to add a certain parameter to "Free Parameters" list, the list where I am saying to CATIA which variables can be changed. If somebody knows why it is happening so, please HELP.