WorkArea start point

...If I call the workAreaStart two times it work properly 😄

activeComp.workAreaStart = 5;

activeComp.workAreaStart = 5;
activeComp.workAreaDuration = 2; 

Ah, OK. That's interesting. It's like you need to reset it first to avoid running into constraints:

var activeComp = app.project.activeItem;
activeComp.workAreaStart = 0;
activeComp.workAreaDuration = activeComp.duration;
activeComp.workAreaStart = 5;
activeComp.workAreaDuration = 2;

My Script should just shift the Work area. 

activeComp.workAreaStart = 5;
activeComp.workAreaDuration = 2; 
But dont work in case 2.

The only thing I'm seeing is that trying to set a duration that extends past the end of the comp will generate an error, but I don't see any behavior that depends on where the CTI is located (is that what you meant)? Can you post a screenshot?