Hi V
When you start a new simulation and go to the Add Securities window there's a Periodicity option in the bottom left corner. You cannot change the periodicity if some securities have already been loaded so remove all securities and then select the securities you want and set the periodicity before clicking the Open button. Any securities added later will use the same periodicity set when opening the initial group. Don't try to change the periodicity of any securities already loaded as you won't be able to. The trick is to remove all securities and then select the periodicity before opening a new group.
Roy