Hi Andrea,
On the Settings Tab for your OPC DA Source Agent, change the Browsing Mode DA 2.05Ato Relative Path, and save. On the Agent Instance that is referencing the OPC DA Source Agent, on the Tag Query Tab, change the Cache Mode to Cache. Save your changes and restart the Agent Instance and you should be able to browse the Tags from PCo, as well as from MII using the TagList Mode of the TagQuery.
Note: It is highly recommended that you obtain or create a Symbol file for each OPC Topci defined in RSLinx so that you can browse tags by a tag name rather than a PLC Address, especially if you are browsing PLC-5 or SLC-5 family PLC addresses. The documentation for the RSLinx Symbol files is in the RSLinx Help.
Regards, Steve