Shift-click to select the lines and arcs that define the contour of the collar. Do not select points, construction lines, dimensions, or constraints.
The group must contain only geometric elements. Make sure there are no relationship handles or other non-essential elements in the group.
Click Group on the Change toolbar.
Activate all layers on which the collar geometry resides. The possible layers are Default, CrossSectionPlane, and BasePlane. Click Layer Status to activate and deactivate layers.