If we gave both PCDI & SCADA address to any one tag and loaded to controller. After loading if u delete that address in particular tag and assign same address to same tag or different tags it wont allow. For using same address use following steps Step1–>Initially unassign PCDI & SCADA address and load to controller Step2–>Now assign same address to same tag or other tags This problem will come when “Online Modification” of controller properties is checked.