Programmatically add and remove person from itshop customers

And of course, always PersonInITShopOrg.XOrigin = 1 :-)

Just an update:

I have tryed this:

Dim new_pis As PersonInITShopOrg = Session.Source.CreateNew(Of PersonInITShopOrg)
new_pis.UID_ITShopOrg = uid_ItShopOrg
new_pis.UID_Person = uid_person
new_pis.AssignDirect()
new_pis.Save(Me.Session)

where uid_ItShopOrg is the customer node of an itshop and uid_person the uid_person of the employee I need to add.

The script runs smoothly, but even if no error is raised, the employee is not put into the ItShop.

So I've tryed on the following:

Dim pis As ISingleDbObject = Me.Connection.CreateSingle("PersonInITShopOrg")
pis.PutValue("UID_Person",uid_person)
pis.PutValue("UID_ITShopOrg", uid_ItShopOrg)
pis.PutValue("XOrigin",1)
pis.Save()

and it works pretty well in some environment but it does not work at all in some others...
Obviously it is complaining that I can't edit XOrigin. The executing user in the second environment probably lacks some rights, but I'm not sure

So the question is: how can i surely add a Person into the customer node if a ITShop?