How is the value of Incident._ClientInterne being set?
Also, you would need to make sure that ClientInterne has a default value set on it, because you are not checking if its null.
A Boolean with no default value can be equal to true, false, or just be null.
Im sure you have a reason for having a Boolean for both, but I would think the easiest solution would be to use the calc you have on ClientInterne currently to set the value to True for your conditions, and otherwise just leave the default setting to False on ClientInterne.