Core Issue
The system administrator can configure the same data as the LAN switch and Emergency Response Location (ERL) administrators, so other users are prevented from logging in for data integrity purposes when the system administrator is logged in.
Resolution
Check the error message to determine the reason for the failed login. If the system administrator is logged in, no one else can log in as a LAN switch or ERL administrator. If the system administrator is not logged in, separate LAN switch and ERL administrators should be able to log in simultaneously.
For more details about troubleshooting Cisco Emergency Responder (Cisco ER), refer to these documents: