Position the cursor on a valid entry

What causes this issue?

You have called a function, which references another line in the list.
The cursor was not positioned in the list.

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?

Position the cursor on a line in the list and select the function
again.

Error message extract from SAP system. Copyright SAP SE.