As I often do, I typed a user's last name in the search bar and lo - they did not exist in LanSweeper. Digging further, even though the user is in AD and active, I see no corresponding record in the AD listing within LanSweeper.
Digging further still, I see this problem repeats for several users in AD:
Looking in "Active Directory Users and Computers" (app in RSAT) <user> shows up in their OU alongside other users. <user> is current (last logged in recently). <user>, however, does not show up in LanSweeper at all. Other users in the OU show up fine in LanSweeper. <user> has a machine which shows up in both "Active Directory Users and Computers" and LanSweeper's listing of machines. I noted that the user's machine has not been successfully scanned by LanSweeper yet, though it's AD record does list in LanSweeper.
I don't see any reason why these users do not appear in LanSweeper - is there a way to get them to show up? When LanSweeper scans AD, what criteria does it use to accept/ignore an AD user record?
