in the Details tab, do you have "Consider Reserved Elements" checked? Having it unchecked would explain the error you describe.
The second error you are getting is because you are using a dictionary object (like volume1) in a spot (the filter) where one of its attributes (volume1.name) would go. Appending .name to the entry field in the finder would fix the syntax, but you'd be right back at your first problem because without a reservation, the filter would again not return any result for that name.
The better way to refer back to the mirror volume would be to get rid of the finder (hit the x next to "Automatically searched") and just put its name in the entry box. Make sure you are actually putting in the dictionary object (volume1) and not one of its attributes (volume1.name).
Hope this helps. If it doesn't, please share your workflow. This would take some of the guesswork out of what your objects and variables are.