Unknown Workstation

i have a problem with my service desk plus

If i click on "workstation" i see :

(service desk.jpg)

and if i click on one server/workstation, in my exemple alpha-test

(service desk2.jpg)

i see Product Name : Unknown Workstation

and if i push on edit, is not unknoown workstation but (service desk3.jpg)

how don't see Unknown Workstation and good name?

Sorry for my poor english