This feature is linked to the Basic data form (Settings tab, Allow negative stock check box). To change the setting of this field, use the Allow negative stock process. This process checks the stock to see whether it is possible to change the setting. For example, if you want to disallow negative stock, you can only do so if no negative stock lines are present. You will receive a notification if the field cannot be changed. This notification will then be added to the log. You can select or clear the check box using the Allow negative stock process.