Select exactly one stage of shipment

What causes this issue?

In the graphics, you have either selected no shipment stages or more
than one shipment stage. However, only one shipment stage can be
selected.

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?

Use the mouse to select the shipment stage, for which you want to
diplay details and then call the desired function.

Error message extract from SAP system. Copyright SAP SE.