This happens when someone has started the End of Day process and then tries to stop it by hitting the refresh. This does not stop EOD, and the inventory gets locked, which is what prevents you from posting your deliveries.
A ServiceDesk ticket is not required.
To action this, open the delivery draft - you will receive an error about the "incorrect business day/inventory locked", but after selecting OK, the draft will open.
Select Delete, which will turn the draft into a scheduled order.
Now, run the End of Day process for one cycle to unlock the inventory, and then you will be able to post your delivery.
Continue to follow the Receiving a Delivery process steps.
Once complete, continue to run the End of Day process to catch up to the current business day.