Hello Greg,
The "Structural elements" filter function is used to find frames created by Structural elements macro like e.g. "Portal frame" macro, "Truss" macro, etc.
So if you get this warning message "No objects found with the name ASTSTRUCTURAL", this is certainly because you have no Structural elements macro(s) in your 3D model.
Just as a reminder: if you want to filter Joint cuboids, you need to use the "Joont boxes" filter function.
Regards
Philippe