Roles should have XMII_ScheduleEditor_all action assigned in order to perform all actions related to scheduler. You need to do this in NWA.
http://<IP address>:<Port>/nwa
Take a look at below link for more understanding on actions.
Actions for Permissions (SAP Library - SAP Manufacturing Integration and Intelligence)
Hope you have SAP_XMII_Developer and SAP_XMII_User roles assigned. Check all these about roles, groups and actions in UME.
Can refer below link for more information of Netweaver,
Netweaver CE Basics for MII - xMII - SCN Wiki
Regards,
Padma Rao