Shipment has open confirmation & (L=Loading, D=Del.Conf.); confirm

What causes this issue?

There are quantities saved without confirmation. The message indicates
whether the quantity comes from Loading (L) or Delivery Confirmation
(D).

System Response

Error; no further processing

How to fix this error?

Confirm the open postings in load or delivery confirmation. You may also
delete the quantity items and confirmation to get to a clear status of
the shipment.

Procedure for System Administrators

The system issues an error message and will not allow you to continue with this transaction until the error is resolved.

Error message extract from SAP system. Copyright SAP SE.