Variants for external programs cannot be displayed

What causes this issue?

You asked the system to display variants of a program that is not part
of the SAP System.
Variants are sets of selection values for SAP programs and reports. The
background processing system can offer support for editing only SAP
ABAP/4 variants.

System Response

No action taken.

How to fix this error?

Error message extract from SAP system. Copyright SAP SE.