The Warnings tab becomes active for both Pick list and Delivery reporting list, if there are any warnings.
Under this tab the warnings generated when creating the pick list or the delivery reporting are displayed collected in one list. These warnings always apply for the rows that have been selected to be displayed in the pick list or delivery reporting. These warnings are also indicated in the pick list or in the delivery list by having the corresponding values presented in red and with a red exclamation mark to the far right. On printed documents the exclamation mark is normally the only warning shown.
You can read more under Printout samples, list type Pick list.