• manually create workstations, using their IP address only.
• go to Assets > Workstations
• select one or more workstations
• Actions > change credentials, just to make sure that credentials are ok; well, they are
• scan workstation window appears and enter correct credentials
• click "save and scan now"
• scanning window appears
• click close and go back to Assets > Workstations

Now, one is expecting to see some update there. Well, it's not. It's the same as you left it.

However, if you go to "New scan" and scan workstations one by one, it works!!