Modification mode: Selected area contains invalid elements

What causes this issue?

You are using the Screen Painter with the Modification Assistant and
have selected an element or group of elements. You want to use a
function that would:
Change the type of the element
For example, converting checkboxes into radio buttons.
Change the assignment of elements to graphical elements (containers)
For example, converting to a step loop or a table control, or forming a
radio button group.
Under the Modification Assistant, these operations are only possible
for screen elements that are not SAP original objects.
There is at least one SAP original element in your selection.

System Response

Operation canceled.

How to fix this error?

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

Procedure for System Administrators

Error message extract from SAP system. Copyright SAP SE.