Solution : https://service.sap.com/sap/support/notes/1652880 (SAP Service marketplace login required)
Key words : 
prerequisites service user password change, service users reason, solution kindly implement, symptom firefighters, target systems, spm launchpad, login screen, target system, firefighter login, causing problems
Related Notes : 
       
| 1640992 | Master Note for SAP Access Control 10.0 - Support Pack 7 |