"You Cannot Delete an Active Network/Adapter Subnet"

Hi all ! . I am using ZonaAlarm version 5.5 ... . Time ago, I set a "Trusted zone", using "Firewall" + "Zone", providing there a Subnet address and Mask, as 192.168.1.4/255.255.255.0 ... . Now, I try to delete it, and receive a message "YOU CANNOT DELETE AN ACTIVE NETWORK" The entry type is "Adapter Subnet" .... . What must I do to delete it ? Yes, I know ... "Inactivate it" ... How do I do to Inactivate this Sunet ?? . Thankx ! .