Object is being edited outside the SAP System

What causes this issue?

The object you want to change was checked out for editing from the SAP
System using an external tool. Changes that you make to this object
while it is checked out will be overwritten when the object is checked
in again.

System Response

You are not authorized to edit an object which is currently checked out.

How to fix this error?

Finish working on the object with the external tool and check the object
in again.

Procedure for System Administrators

The system issues an error message and will not allow you to continue with this transaction until the error is resolved.

Error message extract from SAP system. Copyright SAP SE.