Transaction code not defined

What causes this issue?

You have called up the program without defining a corresponding
transaction code. This is probably beacause variant maintenance has
been called up using se38. It is not possible to create variants using
this transaction.

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?

Procedure for System Administrators

Error message extract from SAP system. Copyright SAP SE.