For linking Active Directory, users must have ftp home folder setup. This is not seen in Active Directory main window. But requires configuration via ADSIedit.msc
This window allow more configuration for the same AD.
Under Attribute Editor (after right-click properties of a user), look up msIIS-FTPDir (specific folder) & msIIS-FTPRoot (root path), set these as the home of the user.
Restart server of FTP.