Block a person on an activity

Hello,

I can not define tasks that are reserved for the defined period - that is, that person only works on that activity and can not be cut by another activity.

I have several projects with different tasks where the same person is assigned (for example regular between 2 dates). I need to add an activity where this person must be on an activity for a period. So I created a task over a period of 5 days with 5 days of charges and putting in regular days. However, he plans me for 6 days, which does not interest me.

Is there a solution to my question?

thank you in advance

The priority of my task is 60. The others on my other projects are 500 and it does not change anything.

I found.
I had to remove the concepts of project and sub-project as well as the notions of activities and sub-activities.
When I change the priority of my task so that the person is booked 5 days out of 5 days, this is the case.