Ladder is missing the top edge reference object. Edit ladder and select a new top edge. The ladder will not respond to any edits until a new top edge is selected. (Structure)
Meaning: The top edge reference object that was specified when the ladder was created has moved or no longer exists in the model. The top edge reference is used to define the top elevation of the ladder. The ladder will not respond to property edits until you select a new top edge.
1. Click Select , and select the ladder.
2. Select Select Top Edge on the ribbon.
3. Select a new top edge reference for the ladder.