Challenge
You want to add more than one component to your CAD assembly in one step.
Solution
This is not valid for all CAD systems, as the API of the CAD system does not support adding multiple components in one step!
Supported CAD systems: AutoCAD and PTC Creo.
Please add in <ECTR configuration>\applications\<CAD system>\customize\config\default.txt
plm.document.addComponent.singleSelectionOnly.<CAD>=false