Scan problem ,it not list all workstation

Scan problem ,it not list all workstation

hello
i have ServiceDesk Plus and connect in to my active directory,i install agent ServiceDesk Plus in all computer.
i have 100user and when i scan it it show me 60 user in workstation list and not exist other40 ones in workstation list ,i can scan 40other user one by one with ip address, it show me the computer detail but not list it on my workstation list?!
how can i fix this problem that add remain user to my workstation list??

                  New to ADSelfService Plus?