The Split Walls window must be populated before any elements can be picked in the 3D view.
From the Connections at split part of the
Split Walls window, you can specify how the ends of the new shorter length walls are to be connected at the split points:
Select the Confirm before splitting check box to display a
Confirm window before each split occurs.
If the Confirm Before Splitting check box was selected, a
Confirm window displays.
Click No to discard any inputs and close the
Confirm window.
Click Cancel to discard any information and close the
Split Walls window.