Thank you.
I tried it with BoundingBoxCenter (before: bounding box center).
No error this time - fine. But also not an operation - ces´t dommage.

My workflow like seen in Pilous video:
1. Making the base ellipse
2. Creating a Center Point (a second object - a tiny circle)
3. Named both as "Base"
4. Made the array along the helix
5. Hided the helix
6. Activated all objects
7. Did with B (my shortcut) the BoundingBoxCenter
...no operation followed

Where is my mistake?