A predefined target element cannot be deleted

What causes this issue?

You have tried to delete the last priority of a target element that is
defined in the interface.
The deletion of target elements is only possible for target elements
that have created dynamically (using the pushbutton 'Create').

System Response

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

How to fix this error?

If you do not want to supply the target element, leave the field for
the data source blank in all the lines for the last priority.

Procedure for System Administrators

Error message extract from SAP system. Copyright SAP SE.