I've looked at your project file and specifically at task 24 and I'm afraid I still don't know what you mean by split baseline.

Task 24 is baselined, although I am not sure why you have a summary task as well as the subtask. You do not have any resources assigned to the task and that is a usual way of splitting a task - edit the timescaled work in the Task Usage view and enter zeros in the work field. But, as you don't have assigned resources you can't do that.

Can you please explain in more detail what you need?