User already exists while adding access through domain group.

Hello Team,

We are trying to provide access to user through Active directory domain group but it showing an error like below:

Task Response: {"type":"error","status":409,"code":"user_login_already_used","help_url":"http:\/\/developers.box.com\/docs\/#errors","message":"User with the specified login already exists","request_id":"g07vnkhsi9liui5p"}