External segment name & cannot be interpreted

What causes this issue?

The external segment name (the segment definition) cannot be shown on
an internal segment type of a particular version. The system,
therefore, does not know how many fields the
<DS:GLOS.Segment>segment</> consists of and which fields these are.

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.