ArcGIS Monitor: A duplicate was found - Operation cannot proceed

Error Message

In ArcGIS Monitor, attempting to register ArcGIS Server or Portal for ArcGIS as a component fails and returns the following error message:

Error:
Error: A duplicate was found - operation cannot proceed

Cause

• Registering ArcGIS Monitor with an existing registration component which has the same name or identifier.
• Registering Portal for ArcGIS on a standby machine.

Solution or Workaround

For ArcGIS Server

In the ArcGIS Server Administrator Directory, delete the monitorSystemId property to remove any existing connection from ArcGIS Monitor.

1. Log in to the ArcGIS Server Administrator Directory with an administrator account using the following URL:

<machine>.<domain>.com/<webadaptorname>/admin

2. Click system.
3. For Resources, click properties.

4. On the System Properties page, click update.
5. On the Update Server Properties page, remove monitorSystemId and click Update.

The second option is to delete the usage report in ArcGIS Server Administrator Directory.

1. Log in to the ArcGIS Server Administrator Directory with an administrator account, and click usagereports.
2. Click a usage report.
3. On the Usage Reports - <name> page, click delete.
4. On the Delete Report page, click Delete.

For Portal for ArcGIS

This is expected behavior when registering a highly available Portal for ArcGIS with ArcGIS Monitor. If Portal for ArcGIS is already registered on the primary machine, it cannot be registered again on the standby machine.