Linking two personnel assignments in IT0709

I could be totally lost and not able to find what is stopping me at this moment to link multiple personnel assignments in IT0709, in my below test conditions.

> Activated MGE (GLEMP/PAUIX/PIDGN-2)

> Example: Generated Peson ID for the first PERNR using the std program to populate IT0709.

> Person ID not generated for his additional assignments in other countries.

> Now trying to link the assignments by creating IT0709 record manually for these other country assignments to add the already generated PERSON ID.

> system do not like this and it tells the person id is already used and should be unique????

Can somebody throw some quick thoughts please..