The last schema change could not be canceled

What causes this issue?

You executed the <LS>Undo</> function during maintenance of the schema
steps. However, no change has been reversed.
Note the following:
You cannot reverse changes you made to the schema header data.
You can reverse changes to fields (if, for example, you selected a
field).
You can reverse the moving of lines or rates.
If you insert or delete rates, you cannot reverse these changes.
This message is also displayed if you have not yet carried out any
changes in the schema steps.

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.