From Object documentation in SU21(B_USERSTAT):
User status authorization object
With this authorization object you protect the setting or deletion of user status in the general status management of orders, projects, network plans, and so on.
This authorization object is only checked during the direct setting or deletion of the user status in the status maintenance screen (SAPLBSVA 0300/0302) or in the dialog box of the user status maintenance (SAPLBSVA 0201).
Ensure the mentioned screens are being used for the activity , if then this object should be cheked.
Thanks,Krishna