Delivery status only allows display mode

What causes this issue?

The delivery status prevents the packing data from being changed.

System Response

The packing dialog was called up in display mode.

How to fix this error?

Check to see whether goods issue was already posted for this delivery
or whether the delivery is incomplete regarding the packing function.

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.