The user can login to BitBucket via browser, but at Sourcetree installation, when he provide the same username and password, together with bitbucket address, it say:
"Failed to check login for user [userxxx]: You do not have permission to access URL 'https://bitbucket.xxxxxxxxxx.com/rest/api/1.0/users/userxxx' please check the user credentials associated with this account. The request returned with status code 'Unauthorized'.