The selected line segment already exists in the graphic

What causes this issue?

The system found exactly one line segment for the selection criteria
you entered. Hoever, this line segment is already contained in the
graphic - either as part of the line or as a line segment that can be
inserted.
As a line segment can only exist in a line once, the system did not
copy the line segment selected to the graphic.

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?

Error message extract from SAP system. Copyright SAP SE.