OPC Items with null reference
Have you performed upload, or did you create the objects/item IDs manually?
I have not (yet) seen the uploader creating a null item from a non-null item ID returned during upload.
The item ID should be visible in the OPCAdapter Basic log of the AdvDsOPCConnector component in afwapplogviewer.exe tool. Sorry, no manual for this tool - I teach some of the techniques in the E143 Troubleshooting System 800xA expert workshop.