I got the error in Fortigate 2000E device event error. So based on this article describes the information about System Event log “Administrator admin login failed from https(127.0.0.1) because of invalid password”
You will getting this event log in every 15 min.
Login failed means you have assigned admin authentication of device Fortigate 2000E in any other device with admin user. First check the mapped device authentication where you assigned admin password.
I found that admin user assigned to FortiAnalyzer. Check the login credentials you have configured on both sides.
-FortiAnalyzer
Go to you Analyzer->Select ADOM -> Device Management -> Edit your Device and edit Admin User and Password.
Same need to verify with other Fortinet device like Forti Sandbox, FortiEMS, FortiClient….etc..
This problem might be occur due to host restriction. if you define trusted hosts for the administrator. You must also add 127.0.0.1/32 as a trusted host.
Network and Security Solutions 
127.0.0.1/32 cannot be added as trusted host. It return Invalid IP address.
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